Chapter XLIX: Part IV: The skeleton of the ventral lobe of the tail fin, and its (2)

There appear to us, however, to be sufficiently serious objections to this view to render it necessary for us to suspend our judgment with reference to this point. In the first place, if the view that the genital ducts are Müllerian ducts is correct, the true genital ducts of _Lepidosteus_ must necessarily be developed at a later period than the secondary attachment between their open mouths and the genital folds, which would, to say the least of it, be a remarkable inversion of the natural order of development. Secondly, the condition of our oldest larva shews that the Müllerian duct, if developed later, is only split off from quite the posterior part of the segmental duct; yet in all types in which the development of the Müllerian duct has been followed, its anterior extremity, with the abdominal opening, is split off from either the foremost or nearly the foremost part of the segmental duct.

Judging from the structure of the adult genital ducts of other Ganoids they must also be developed only from the posterior part of the segmental duct, and this peculiarity so struck one of us that in a previous paper[545] the suggestion was put forward that the true Ganoid genital ducts were perhaps not Müllerian ducts, but enlarged segmental tubes with persisting abdominal funnels belonging to the mesonephros.

Footnote 545: F. M. Balfour, "On the Origin and History of the
Urinogenital Organs of Vertebrates," _Journ. of Anat. and
Phys._, Vol. X., 1876 [This edition, No. VII].

If the possibility of the oviduct of _Lepidosteus_ not being a Müllerian duct is admitted, a similar doubt must also exist as to the genital ducts of other Ganoids, and we must be prepared to shew that there is a reasonable ground for scepticism on this point. We would in this connexion point out that the second of the two arguments urged against the view that the genital duct of _Lepidosteus_ is not a Müllerian duct applies with equal force to the case of all other Ganoids.

The short funnel-shaped genital duct of the Chondrostei is also very unlike undoubted Müllerian ducts, and could moreover easily be conceived as originating by a fold of the peritoneum, a slight extension of which would give rise to a genital duct like that of _Lepidosteus_.

The main difficulty of the view that the genital ducts of Ganoids are not Müllerian ducts lies in the fact that they open into the segmental duct. While it is easy to understand the genesis of a duct from a folding of the peritoneum, and also easy to understand how such a duct might lead to the exterior by coalescing, for instance, with an abdominal pore, it is not easy to see how such a duct could acquire a communication with the segmental duct.

We do not under these circumstances wish to speak dogmatically, either in favour of or against the view that the genital ducts of Ganoids are Müllerian ducts. Their ontogeny would be conclusive on this matter, and we trust that some of the anatomists who have the opportunity of studying the development of the Sturgeon will soon let us know the facts of the case. If there are persisting funnels of the mesonephric segmental tubes in adult Sturgeons, some of them ought to be situated within the genital ducts, if the latter are not Müllerian ducts; and naturalists who have the opportunity ought also to look out for such openings.

The mode of origin of the anterior part of the genital duct of _Lepidosteus_ appears to us to tell strongly in favour of the view, already regarded as probable by one of us[546], that the Teleostean genital ducts are derived from those of Ganoids; and if, as appears to us indubitable, the most primitive type of Ganoid genital ducts is found in the Chondrostei, it is interesting to notice that the remaining Ganoids present in various ways approximations to the arrangement typically found in Teleostei. _Lepidosteus_ obviously approaches Teleostei in the fact of the ovarian ridge forming part of the wall of the oviduct, but differs from the Teleostei in the fact of the oviduct opening into the kidney ducts, instead of each pair of ducts having an independent opening in the cloaca, and in the fact that the male genital products are not carried to the exterior by a duct homologous with the oviduct. _Amia_ is closer to the Teleostei in the arrangement of the posterior part of the genital ducts, in that the two genital ducts coalesce posteriorly; while _Polypterus_ approaches still nearer to the Teleostei in the fact that the two genital ducts and the two kidney ducts unite with each other before they join; and in order to convert this arrangement into that characteristic of the Teleostei we have only to conceive the coalesced ducts of the kidneys acquiring an independent opening into the cloaca behind the genital opening.

Footnote 546: F. M. Balfour, _Comparative Embryology_,
Vol. II., p. 605 [the original edition].

_The male genital ducts._--The discovery of the vasa efferentia in _Lepidosteus_, carrying off the semen from the testis, and transporting it to the mesonephros, and thence through the mesonephric tubes to the segmental duct, must be regarded as the most important of our results on the excretory system.

It proves in the first place that the transportation outwards of the genital products of both sexes by homologous ducts, which has been hitherto held to be universal in Ganoids, and which, in the absence of evidence to the contrary, must still be assumed to be true for all Ganoids except _Lepidosteus_, is a secondary arrangement. This conclusion follows from the fact that in Elasmobranchii, &c., which are not descendants of the Ganoids, the same arrangement of seminal ducts is found as in _Lepidosteus_, and it must therefore have been inherited from an ancestor common to the two groups.

If, therefore, the current statements about the generative ducts of Ganoids are true, the males must have lost their vasa efferentia, and the function of vas deferens must have been taken by the homologue of the oviduct, presumably present in the male. The Teleostei must, moreover, have sprung from Ganoidei in which the vasa efferentia had become aborted.

Considerable phylogenetic difficulties as to the relationships of Ganoidei and Elasmobranchii are removed by the discovery that Ganoids were originally provided with a system of vasa efferentia like that of Elasmobranchii.

THE ALIMENTARY CANAL AND ITS APPENDAGES.

I.--_Anatomy._

Agassiz (No. 2) gives a short description with a figure of the viscera of _Lepidosteus_ as a whole. Van der Hoeven has also given a figure of them in his memoir on the air-bladder of this form (No. 8), and Johannes Müller first detected the spiral valve and gave a short account of it in his memoir (No. 13). Stannius, again, makes several references to the viscera of _Lepidosteus_ in his anatomy of the Vertebrata, and throws some doubt on Müller's determination of the spiral valve.

The following description refers to a female _Lepidosteus_ of 100.5 centims. (Plate 40, fig. 66).

With reference to the mouth and pharynx, we have nothing special to remark. Immediately behind the pharynx there comes an elongated tube, which is not divisible into stomach and oesophagus, and may be called the stomach (_st._). It is about 44.6 centims. long, and gradually narrows from the middle towards the hinder or pyloric extremity. It runs straight backwards for the greater part of its length, the last 3.8 centims., however, taking a sudden bend forwards. For about half its length the walls are thin, and the mucous membrane is smooth; in the posterior half the walls are thick, and the mucous membrane is raised into numerous longitudinal ridges. The peculiar glandular structure of the epithelium of this part in the embryo is shewn in Plate 40, fig. 62 (_st._). Its opening into the duodenum is provided with a very distinct pyloric valve (_py._). This valve projects into a kind of chamber, freely communicating with the duodenum, and containing four large pits (_c´_), into each of which a group of pyloric cæca opens. These cæca form a fairly compact gland (_c._) about 6.5 centims. long, which overlaps the stomach anteriorly, and the duodenum posteriorly.

Close to the pyloric valve, on its right side, is a small papilla, on the apex of which the bile duct opens (_b.d´_).

A small, apparently glandular, mass closely connected with the bile duct, in the position in which we have seen the pancreas in the larva (Plate 40, figs. 62 and 63, _p._), is almost certainly a rudimentary pancreas, like that of many Teleostei; but its preservation was too bad for histological examination. We believe that the pancreas of _Lepidosteus_ has hitherto been overlooked.

The small intestine passes straight backwards for about 8 centims., and then presents three compact coils. From the end of these a section, about 5 centims. long, the walls of which are much thicker, runs forwards. The intestine then again turns backwards, making one spiral coil. This spiral part passes directly, without any sharp line of demarcation, into a short and straight tube, which tapers slightly from before backwards, and ends at the anus. The mucous membrane of the intestine for about the first 3.5 centims. is smooth, and the muscular walls thin: the rest of the small intestine has thick walls, and the mucous membrane is reticulated.

A short spiral valve (_sp.v._), with a very rudimentary epithelial fold, making nearly two turns, begins in about the posterior half of the spiral coil of the intestine, extending backwards for slightly less than half the straight terminal portion of the intestine, and ending 4 centims. in front of the anus. Its total length in one example was about 4.5 centims.

The termination of the spiral valve is marked by a slight constriction, and we may call the straight portion of the intestine behind it the rectum (_rc._).

The posterior part of the intestine, from the beginning of the spiral valve to the anus, _is connected with the ventral wall of the abdomen by a mesentery_.

The air-bladder (_a.b._) is 45 centims. long, and opens into the alimentary canal by a slit-like aperture (_a.b´._) on the median dorsal line, immediately behind the epipharyngeal teeth. Each lip of this aperture is largely formed by a muscular cushion, thickest at its posterior end, and extending about 6 millims. behind the aperture itself. A narrow passage is bounded by these muscular walls, which opens dorsally into the air-bladder.

The air-bladder is provided with two short anterior cornua, and tapers to a point behind: it shews no indication of any separation into two parts. A strong band of connective tissue runs along the inner aspect of its whole dorsal region, from which there are given off on each side--at intervals of about 12 millims. anteriorly, gradually increasing to 18 millims. posteriorly--bands of muscle, which pass outwards towards its side walls, and then spread out into the numerous reticulations with which the air-bladder is lined throughout. By the contraction of these muscles the cavity of the air-bladder can doubtless be very much diminished.

The main muscular bands circumscribe a series of more or less complete chambers, which were about twenty-seven in number on each side in our example. The chambers are confined to the sides, so that there is a continuous cavity running through the central part of the organ. The whole organ has the characteristic structure of a simple lung.

The liver (_lr._) consists of a single elongated lobe, about 32 centims. long, tapering anteriorly and posteriorly, the anterior half being on the average twice as thick as the posterior half. The gall-bladder (_g.b._) lies at its posterior end, and is of considerable size, tapering gradually so as to pass insensibly into the bile duct. The hepatic duct (_hp.d._) opens into the gall-bladder at its anterior end.

The spleen (_s._) is a large, compact, double gland, one lobe lying in the turn of the intestine immediately above the spiral valve, and the other on the opposite side of the intestine, so that the intestine is nearly embraced between the two lobes.

II.--_Development._

We have already described in detail the first formation of the alimentary tract so far as we have been able to work it out, and we need only say here that the anterior and posterior ends of the canal become first formed, and that these two parts gradually elongate, so as to approach each other; the growth of the posterior part is, however, the most rapid. The junction of the two parts takes place a very short distance behind the opening of the bile duct into the intestine.

For some time after the two parts of the alimentary tract have nearly met, the ventral wall of the canal at this point is not closed; so that there is left a passage between the alimentary canal and the yolk-sack, which forms a vitelline duct.

After the yolk-sack has ceased to be visible as an external appendage it still persists within the abdominal cavity. It has, however, by this stage ceased to communicate with the gut, so that the eventual absorption of the yolk is no doubt entirely effected by the vitelline vessels. At these later stages of development we have noticed that numerous yolk nuclei, like those met with in Teleostei and Elasmobranchii[547], are still to be found in the yolk.

Footnote 547: For a history of similar nuclei, vide _Comp.
Embryol._, Vol. II., chapters III. and IV.

It will be convenient to treat the history of sections of the alimentary tract in front of and behind the vitelline duct separately. The former gives rise to the pharyngeal region, the oesophagus, the stomach, and the duodenum.

The pharyngeal region, immediately after it has become established, gives rise to a series of paired pouches. These may be called the branchial pouches, and are placed between the successive branchial arches. The first or hyomandibular pouch, placed between the mandibular and hyoid arches, has rather the character of a double layer of hypoblast than of a true pouch, though in parts a slight space is developed between its two walls. It is shewn in section in Plate 37, fig. 43 (_h.m._), from an embryo of about 10 millims., shortly before hatching. It does not appear to undergo any further development, and, so far as we can make out, disappears shortly after the embryo is hatched, without acquiring an opening to the exterior.

It is important to notice that this cleft, which in the cartilaginous Ganoids and _Polypterus_ remains permanently open as the spiracle, is rudimentary even in the embryo of _Lepidosteus_.

The second pouch is the hyobranchial pouch: its outer end meets the epiblast before the larva is hatched, and a perforation is effected at the junction of the two layers, converting the pouch into a visceral cleft.

Behind the hyobranchial pouch there are four branchial pouches, which become perforated and converted into branchial clefts shortly after hatching.

The region of the oesophagus following the pharynx is not separated from the stomach, unless a glandular posterior region (vide description of adult) be regarded as the stomach, a non-glandular anterior region forming the oesophagus. The lumen of this part appears to be all but obliterated in the stages immediately before hatching, giving rise for a short period to a solid oesophagus like that of Elasmobranchii and Teleostei[548].

Footnote 548: Vide _Comp. Embryol._, Vol. II., pp. 50-63 [the
original edition].

From the anterior part of the region immediately behind the pharynx the air-bladder arises as a dorsal unpaired diverticulum. From the very first it has an elongated slit-like mouth (Plate 40, fig. 64, _a.b´._), and is placed in the mesenteric attachment of the part of the throat from which it springs.

We have first noticed it in the stages immediately after hatching. At first very short and narrow, it grows in succeeding stages longer and wider, making its way backwards in the mesentery of the alimentary tract (Plate 40, fig. 65, _a.b._). In the larva of a month and a half old (26 millims.) it has still a perfectly simple form, and is without traces of its adult lung-like structure; but in the larva of 11 centims. it has the typical adult structure.

The stomach is at first quite straight, but shortly after the larva is hatched its posterior end becomes bent ventralwards and forwards, so that the flexure of its posterior end (present in the adult) is very early established. The stomach is continuous behind with the duodenum, the commencement of which is indicated by the opening of the bile duct.

The liver is the first-formed alimentary gland, and is already a compact body before the larva is hatched. We have nothing to say with reference to its development, except that it exhibits the same simple structure in the embryo that it does in the adult.

A more interesting glandular body is the pancreas. It has already been stated that in the adult we have recognized a small body which we believe to be the pancreas, but that we were unable to study its histological characters.

In the embryo there is a well-developed pancreas which arises in the same position and the same manner as in those Vertebrata in which the pancreas is an important gland in the adult.

We have first noticed the pancreas in a stage shortly after hatching (Plate 40, fig. 61, _p._). It then has the form of a funnel-shaped diverticulum of the _dorsal_ wall of the duodenum, immediately behind the level of the opening of the bile duct. From the apex of this funnel numerous small glandular tubuli soon sprout out.

The similarity in the development of the pancreas in _Lepidosteus_ to that of the same gland in Elasmobranchii is very striking[549].

Footnote 549: Vide F. M. Balfour, "Monograph on Development of
Elasmobranch Fishes," p. 226 [This edition, No. X., p. 454].

The pancreas at a later stage is placed immediately behind the end of the liver in a loop formed by the pyloric section of the stomach (Plate 40, fig. 62, _p._). During larval life it constitutes a considerable gland, the anterior end of which partly envelopes the bile duct (Plate 40, fig. 63, _p._).

Considering the undoubted affinities between _Lepidosteus_ and the Teleostei, the facts just recorded with reference to the pancreas appear to us to demonstrate that the small size and occasional absence (?) of this gland in Teleostei is a result of the degeneration of this gland; and it seems probable that the pancreas will be found in the larvæ of most Teleostei. These conclusions render intelligible, moreover, the great development of the pancreas in the Elasmobranchii.

We have first noticed the pyloric cæca arising as outgrowths of the duodenum in larvæ of about three weeks old, and they become rapidly longer and more prominent (Plate 40, fig. 62, _c._).

The portion of the intestine behind the vitelline duct is, as in all the Vertebrata, at first straight. In Elasmobranchii the lumen of the part of the intestine in which a spiral valve is present in the adult, very early acquires a more or less semilunar form by the appearance of a fold which winds in a long spiral. In _Lepidosteus_ there is a fold similar in every respect (Plate 38, fig. 53, _sp.v._), forming an open spiral round the intestine. This fold is the first indication of the spiral valve, but it is relatively very much later in its appearance than in Elasmobranchii, not being formed till about three weeks after hatching. It is, moreover, in correlation with the small extent of the spiral valve of the adult, confined to a much smaller portion of the intestine than in Elasmobranchii, although owing to the relative straightness of the anterior part of the intestine it is proportionately longer in the embryo than in the adult.

The similarity of the embryonic spiral valve of _Lepidosteus_ to that of Elasmobranchii shews that Stannius' hesitation in accepting Müller's discovery of the spiral valve in _Lepidosteus_ is not justified.

J. Müller (_Bau u. Entwick. d. Myxinoiden_) holds that the so-called bursa entiana of Elasmobranchii (_i.e._, the chamber placed between the part of the intestine with the spiral valve and the end of the pylorus) is the homologue of the more elongated portion of the small intestine which occupies a similar position in the Sturgeon. This portion of the small intestine is no doubt homologous with the still more elongated and coiled portion of the small intestine in _Lepidosteus_ placed between the chamber into which the pyloric cæca, &c., open and the region of the spiral valve. The fact that the vitelline duct in the embryo _Lepidosteus_ is placed close to the pyloric end of the stomach, and that the greater portion of the small intestine is derived from part of the alimentary canal behind this, shews that Müller is mistaken in attempting to homologise the bursa entiana of Elasmobranchii, which is placed in front of the vitelline duct, with the coiled part of the small intestine of the above forms. The latter is either derived from an elongation of the very short portion of the intestine between the vitelline duct and the primitive spiral valve, or more probably by the conversion of the anterior part of the intestine, originally provided with a spiral valve into a coiled small intestine not so provided.

We have already called attention to the peculiar mesentery present in the adult attaching the posterior straight part of the intestine to the ventral wall of the body. This mesentery, which together with the dorsal mesentery divides the hinder section of the body-cavity into two lateral compartments is, we believe, a persisting portion of the ventral mesentery which, as pointed out by one of us[550], is primitively present for the whole length of the body-cavity. The persistence of such a large section of it as that found in the adult _Lepidosteus_ is, so far as we know, quite exceptional. This mesentery is shewn in section in the embryo in Plate 38, fig. 53 (_v.mt._). The small vessel in it appears to be the remnant of the subintestinal vein.

Footnote 550: _Comparative Embryology_, Vol. II. p. 514 [the
original edition].

THE GILL ON THE HYOID ARCH.

It is well known that _Lepidosteus_ is provided with a gill on the hyoid arch, divided on each side into two parts. An excellent figure of this gill is given by Müller (No. 13, plate 5, fig. 6), who holds from a consideration of the vascular supply that the two parts of this gill represent respectively the hyoid gill and the mandibular gill (called by Müller pseudobranch). Müller's views on this subject have not usually been accepted, but it is the fashion to regard the whole of the gill as the hyoid gill divided into two parts. It appeared to us not improbable that embryology might throw some light on the history of this gill, and accordingly we kept a look out in our embryos for traces of gills on the hyoid and mandibular arches. The results we have arrived at are purely negative, but are not the less surprising for this fact. The hyomandibular cleft as shewn above, is never fully developed, and early undergoes a complete atrophy--a fact which is, on the whole, against Müller's view; but what astonished us most in connection with the gill in question is that we have been unable to find any trace of it even in the oldest larva whose head we have had (26 millims.), and at a period when the gills on the hinder arches have reached their full development.

We imagined the gill in question to be the remnant of a gill fully formed in extinct Ganoid types, and therefore expected to find it better developed in the larva than in the adult. That the contrary is the fact appears to us fairly certain, although we cannot at present offer any explanation of it.

SYSTEMATIC POSITION OF LEPIDOSTEUS.

A. Agassiz concludes his memoir on the development of _Lepidosteus_ by pointing out that in spite of certain affinities in other directions this form is "not so far removed from the bony Fishes as has been supposed." Our own observations go far to confirm Agassiz' opinion.

Apart from the complete segmentation, the general development of _Lepidosteus_ is strikingly Teleostean. In addition to the general Teleostean features of the embryo and larva, which can only be appreciated by those who have had an opportunity of practically working at the subject, we may point to the following developmental features[551] as indicative of Teleostean affinities:--

Footnote 551: The features enumerated above are not in all
cases confined to _Lepidosteus_ and Teleostei, but are always
eminently characteristic of the latter.

(1) The formation of the nervous system as a solid keel of the epiblast.

(2) The division of the epiblast into a nervous and epidermic stratum.

(3) The mode of development of the gut (vide pp. 752-754).

(4) The mode of development of the pronephros; though, as shewn on p. 822, the pronephros of _Lepidosteus_ has primitive characters not retained by Teleostei.

(5) The early stages in the development of the vertebral column (vide p. 779).

In addition to these, so to speak, purely embryonic characters there are not a few important adult characters:--

(1) The continuity of the oviducts with the genital glands.

(2) The small size of the pancreas, and the presence of numerous so-called pancreatic cæca.

(3) The somewhat coiled small intestine.

(4) Certain characters of the brain, _e.g._, the large size of the cerebellum; the presence of the so-called lobi inferiores on the infundibulum; and of tori semicirculares in the mid-brain.

In spite of the undoubtedly important list of features to which we have just called attention, a list containing not less important characters, both embryological and adult, separating _Lepidosteus_ from the Teleostei, can be drawn up:--

(1) The character of the truncus arteriosus.

(2) The fact of the genital ducts joining the ureters.

(3) The presence of vasa efferentia in the male carrying the semen from the testes to the kidney, and through the tubules of the latter into the kidney duct.

(4) The presence of a well-developed opercular gill.

(5) The presence of a spiral valve; though this character may possibly break down with the extension of our knowledge.

(6) The typical Ganoid characters of the thalamencephalon and the cerebral hemispheres (vide pp. 769 and 770).

(7) The chiasma of the optic nerves.

(8) The absence of a pecten, and presence of a vascular membrane between the vitreous humour and the retina.

(9) The opisthocoelous form of the vertebræ.

(10) The articulation of the ventral parts of the hæmal arches of the tail with processes of the vertebral column.

(11) The absence of a division of the muscles into dorso-lateral and ventro-lateral divisions.

(12) The complete segmentation of the ovum.

The list just given appears to us sufficient to demonstrate that _Lepidosteus_ cannot be classed with the Teleostei; and we hold that Müller's view is correct, according to which _Lepidosteus_ is a true Ganoid.

The existence of the Ganoids as a distinct group has, however, recently been challenged by so distinguished an Ichthyologist as Günther, and it may therefore be well to consider how far the group as defined by Müller is a natural one for living forms[552], and how far recent researches enable us to improve upon Müller's definitions. In his classical memoir (No. 13) the characters of the Ganoids are thus shortly stated:--

"These Fishes are either provided with plate-like angular or rounded
cement-covered scales, or they bear osseous plates, or are quite
naked. The fins are often, but not always, beset with a double or
single row of spinous plates or splints. The caudal fin occasionally
embraces in its upper lobe the end of the vertebral column, which may
be prolonged to the end of the upper lobe. Their double nasal openings
resemble those of Teleostei. The gills are free, and lie in a
branchial cavity under an operculum, like those of Teleostei. Many of
them have an accessory organ of respiration, in the form of an
opercular gill, which is distinct from the pseudobranch, and can be
present together with the latter; many also have spiracles like
Elasmobranchii. They have many valves in the stem of the aorta like
the latter, also a muscular coat in the stem of the aorta. Their ova
are transported from the abdominal cavity by oviducts. Their optic
nerves do not cross each other. The intestine is often provided with a
spiral valve, like Elasmobranchii. They have a swimming-bladder with a
duct, like many Teleostei. Their pelvic fins are abdominal.

"If we include in a definition only those characters which are
invariable, the Ganoids may be shortly defined as being those Fish
with numerous valves to the stem of the aorta, which is also provided
with a muscular coat; with free gills and an operculum, and with
abdominal pelvic fins."

Footnote 552: We do not profess to be able to discuss this
question for extinct forms of Fish, though of course it is a
necessary consequence of the theory of descent that the various
groups should merge into each other as we go back in geological
time.

To these distinctive characters, he adds in an appendix to his paper, the presence of the spiral valve, and the absence of a processus falciformis and a choroid gland.

To the distinctive set of characters given by Müller we may probably add the following:--

(1) Oviducts and urinary ducts always unite, and open by a common urinogenital aperture behind the anus.

(2) Skull hyostylic.

(3) Segmentation complete in the types so far investigated, though perhaps _Amia_ may be found to resemble the Teleostei in this particular.

(4) A pronephros of the Teleostean type present in the larva.

(5) Thalamencephalon very large and well developed.

(6) The ventricle in the posterior part of the cerebrum is not divided behind into lateral halves, the roof of the undivided part being extremely thin.

(7) Abdominal pores always present.

The great number of characters just given are amply sufficient to differentiate the Ganoids as a group; but, curiously enough, the only characters amongst the whole series which have been given, which can be regarded as peculiar to the Ganoids, are (1) the characters of the brain, and (2) the fact of the oviducts and kidney ducts uniting together and opening by a common pore to the exterior.

This absence of characters peculiar to the Ganoids is an indication of how widely separated in organization are the different members of this great group.

At the same time, the only group with which existing Ganoids have close affinities is the Teleostei. The points they have in common with the Elasmobranchii are merely such as are due to the fact that both retain numerous primitive Vertebrate characters[553], and the gulf which really separates them is very wide.

Footnote 553: As instances of this we may cite (1) the spiral
valve; (2) the frequent presence of a spiracle; (3) the
frequent presence of a communication between the pericardium
and the body-cavity; (4) the heterocercal tail.

There is again no indication of any close affinity between the Dipnoi and, at any rate, existing Ganoids.

Like the Ganoids, the Dipnoi are no doubt remnants of a very primitive stock; but in the conversion of the air-bladder into a true lung, the highly specialized character of their limbs[554], their peculiar autostylic skulls, the fact of their ventral nasal openings leading directly into the mouth, their multisegmented bars (interspinous bars), directly prolonged from the neural and hæmal arches and supporting the fin-rays of the unpaired dorsal and ventral fins, and their well-developed cerebral hemispheres, very unlike those of Ganoids and approaching the Amphibian type, they form a very well-defined group, and one very distinctly separated from the Ganoids.

Footnote 554: Vide F. M. Balfour, "On the Development of the
Skeleton of the Paired Fins of Elasmobranchii," _Proc. Zool.
Soc._, 1881 [This edition, No. XX.].

No doubt the Chondrostean Ganoids are nearly as far removed from the Teleostei as from the Dipnoi, but the links uniting these Ganoids with the Teleostei have been so fully preserved in the existing fauna of the globe, that the two groups almost run into each other. If, in fact, we were anxious to make any radical change in the ordinary classification of Fishes, it would be by uniting the Teleostei and Ganoids, or rather constituting the Teleostei into one of the sub-groups of the Ganoids, equivalent to the Chondrostei. We do not recommend such an arrangement, which in view of the great preponderance of the Teleostei amongst living Fishes would be highly inconvenient, but the step from _Amia_ to the Teleostei is certainly not so great as that from the Chondrostei to _Amia_, and is undoubtedly less than that from the Selachii to the Holocephali.

LIST OF MEMOIRS ON THE ANATOMY AND DEVELOPMENT OF LEPIDOSTEUS.

1. Agassiz, A. "The Development of _Lepidosteus_." Part 1., _Proc. Amer. Acad. Arts and Sciences_, Vol. XIV. 1879.

2. Agassiz, L. _Recherches s. l. Poissons Fossiles._ Neuchatel. 1833-45.

3. Boas, J. E. "Ueber Herz u. Arterienbogen bei _Ceradotus_ u. _Protopterus_," _Morphol. Jahrbuch_, Vol. VI. 1880.

4. Davidoff, M. von. "Beiträge z. vergleich. Anat. d. hinteren Gliedmassen d. Fische," _Morphol. Jahrbuch_, Vol. VI. 1880.

5. Gegenbaur, C. _Untersuch. z. vergleich. Anat. d. Wirbelthiere_, Heft II., _Schultergürtel d. Wirbelthiere. Brustflosse der Fische_. Leipzig, 1865.

6. Gegenbaur, C. "Zur Entwick. d. Wirbelsäule d. _Lepidosteus_, &c." _Jenaische Zeitschrift_, Vol. III. 1867.

7. Hertwig, O. "Ueber d. Hautskelet d. Fische (_Lepidosteus_ u. _Polypterus_)," _Morphol. Jahrbuch_, Vol. V. 1879.

8. Hoeven, Van der. "Ueber d. zellige Schwimmblase d. _Lepidosteus_." Müller's _Archiv_, 1841.

9. Hyrtl, J. "Ueber d. Schwimmblase von _Lepidosteus osseus_," _Sitz. d. Wiener Akad._ Vol. VIII. 1852.

10. Hyrtl, J. "Ueber d. Pori abdominales, d. Kiemen-Arterien, u. d. Glandula thyroidea d. Ganoiden," _Sitz. d. Wiener Akad._ Vol. VIII. 1852.

11. Hyrtl, J. _Ueber d. Zusammenhang d. Geschlechts u. Harnwerkzeuge bei d. Ganoiden_, Wien, 1855.

12. Kölliker, A. _Ueber d. Ende d. Wirbelsäule b. Ganoiden_, Leipzig, 1860.

13. Müller, J. "Ueber d. Bau u. d. Grenzen d. Ganoiden," _Berlin Akad._ 1844.

14. Schneider, H. "Ueber d. Augenmuskelnerven d. Ganoiden," _Jenaische Zeitschrift_, Vol. XV. 1881.

15. Wilder, Burt G. "Notes on the North American Ganoids, _Amia_, _Lepidosteus_, _Acipenser_, and _Polyodon_." _Proc. Amer. Assoc. for the Advancement of Science_, 1875.

LIST OF REFERENCE LETTERS.

_a._ Anus. _ab._ Air-bladder. _ab´._ Aperture of air-bladder into throat. _ac._ Anterior commissure. _af._ Anal fin. _al._ Alimentary canal. _ao._ Aorta. _ar._ Artery. _au._ Auditory pit. _b._ Brain. _bc._ Body-cavity. _bd._ Bile duct. _bd´._ Aperture of bile duct into duodenum. _bl._ Coalesced portion of segmental ducts, forming urinogenital bladder. _bra._ Branchial arches. _brc._ Branchial clefts. _c._ Pyloric caæca. _c´._ Apertures of caæca into duodenum. _cb._ Cerebellum. _cdv._ Cardinal vein. _ce._ Cerebrum: in figs. 47A and B, anterior lobe of cerebrum. _ce´._ Posterior lobe of cerebrum. _cf._ Caudal fin. _cn._ Centrum. _ch._ Choroidal fissure. _crv._ Circular vein of vascular membrane of eye. _csh._ Cuticular sheath of notochord. _cv._ Caudal vein. _d._ Duodenum. _dc._ Dorsal cartilage of neural arch. _df._ Dermal fin-rays. _dl._ Dorsal lobe of caudal fin. _dlf._ Dorsal fin. _e._ Eye. _ed._ Epidermis. _ep._ Epiblast. _fb._ Fore-brain. _fe._ Pyriform bodies surrounding the zona radiata of the ovum, probably the remains of epithelial cells. _gb._ Gall-bladder. _gd._ Genital duct. _gl._ Glomerulus. _gr._ Genital ridge. _h._ Heart. _ha._ Hæmal arch. _hb._ Hind-brain. _hc._ Head-cavity. _hpd._ Hepatic duct. _hm._ Hyomandibular cleft. _hop._ Operculum. _hy._ Hypoblast; in fig. 10, hyoid arch. _hyl._ Hyaloid membrane. _ic._ Intercalated cartilaginous elements of the neural arches. _in._ Infundibulum. _ir._ Iris. _is._ Interspinous cartilage or bones. _iv._ subintestinal vein. _ivr._ Intervertebral ring of cartilage. _k._ Kidney. _l._ Lens. _lc._ Longitudinal canal, formed by union of the vasa efferentia. _lin._ Lobi inferiores. _ll._ Ligamentum longitudinale superius. _lr._ Liver. _lt._ Lateral line. _ly._ Lymphatic body in front of kidney. _m._ Mouth. _mb._ Mid-brain. _mc._ Medullary cord. _mel._ Membrana elastica externa. _mes._ Mesorchium. _mn._ Mandible. _md._ and _mo._ Medulla oblongata. _ms._ Mesoblast. _na._ Neural arch. _na´._ Dorsal element of neural arch. _nc._ Notochord. _nve._ Network formed by vasa efferentia on inner face of testis. _od._ Oviduct. _od´._ Aperture of oviduct into bladder. _ol._ Nasal pit or aperture. _olf._ Olfactory lobe. _op._ Optic vesicle. _op ch._ Optic chiasma. _opl._ Optic lobes. _op th._ Optic thalami. _or ep._ Oral epithelium. _ov._ Ovary. _p._ Pancreas. _pc._ Pericardium. _pcf._ Pectoral fin. _pch._ Pigmented layer of choroid. _pf._ Peritoneal funnel of segmental tube of mesonephros. _pfp._ Peritoneal funnel leading into pronephric chamber. _pg._ Pectoral girdle. _plf._ Pelvic fin. _pn._ Pineal gland. _po._ Primitive germinal cells. _pr._ Mesoblastic somite. _prc._ Pronephric chamber. _prn._ Pronephros. _pr n´._ Opening of pronephros into pronephric chamber. _pt._ Pituitary body. _py._ Pyloric valve. _pz._ Parietal zone of blastoderm. _r._ Rostrum. _rb._ Rib. _rc._ Rectum. _s._ Spleen. _sc._ Seminal vessels passing from the longitudinal canal into the kidney. _sd._ Suctorial disc. _sg._ Segmental or archinephric duct. _sgt._ Segmental tubules. _sh._ Granular outer portion of the sheath of the notochord in the vertebral regions. _smx._ Superior maxillary process. _snc._ subnotochordal rod. _so._ Somatic mesoblast. _sp._ Splanchnic mesoblast. _spn._ Spinal nerve. _spv._ Spiral valve. _st._ Stomach. _st._ Seminal tubes of the testis. _sup._ Suctorial papillæ. _t._ Testis. _th._ Thalamencephalon. _thl._ Lobes of the roof of the thalamencephalon. _tr._ Trabeculæ. _ug._ Urinogenital aperture. _v._ Ventricle. _ve._ Vasa efferentia. _vh._ Vitreous humour. _vl._ Ventral lobe of the caudal fin. _vmt._ Ventral mesentery. _vn._ Vein. _vs._ Blood-vessel. _vsh._ Vascular sheath between the hyaloid membrane and the vitreous humour. _vth._ Vesicle of the thalamencephalon. _x._ Groove in epiblast, probably formed in process of hardening. _y._ Yolk. _z._ Commissure in front of pineal gland. _zr._ Outer striated portion of investing membrane (zona radiata) of ovum. _zr´._ Inner non-striated portion of investing membrane of ovum. I. Olfactory nerve. II. Optic nerve. III. Oculomotor nerve. V. Trigeminal nerve. VIII. Facial and auditory nerves.

EXPLANATION OF PLATES 34-42.

PLATE 34.

Figs. 1-4. Different stages in the segmentation of the ovum.

Fig. 1. Ovum with a single vertical furrow, from above.

Fig. 2. Ovum with two vertical furrows, from above.

Fig. 3. Side view of an ovum with a completely formed blastodermic
disc.

Fig. 4. The same ovum as fig. 3, from below, shewing four vertical
furrows nearly meeting at the vegetative pole.

Figs. 5-10. External views of embryos up to time of hatching.

Fig. 5. Embryo, 3.5 millims. long, third day after impregnation.

Fig. 6. Embryo on the fifth day after impregnation.

Fig. 7. Posterior part of same embryo as fig. 6, shewing tail
swelling.

Fig. 8. Embryo on the sixth day after impregnation.

Fig. 9. Embryo on the seventh day after impregnation.

Fig. 10. Embryo on the eleventh day after impregnation (shortly before
hatching).

Fig. 11. Head of embryo about the same age as fig. 10, ventral aspect.

Fig. 12. Side view of a larva about 11 millims. in length, shortly after hatching.

Fig. 13. Head of a larva about the same age as fig. 12, ventral aspect.

Fig. 14. Side view of a larva about 15 millims. long, five days after hatching.

Fig. 15. Head of a larva 23 millims. in length.

Fig. 16. Tail of a larva 11 centims. in length.

Fig. 17. Transverse section through the egg-membranes of a just-laid ovum.

We are indebted to Professor W. K. Parker for figs. 12, 14 and 15.

PLATE 35.

Figs. 18-22. Transverse sections of embryo on the third day after impregnation.

Fig. 18. Through head, shewing the medullary keel.

Fig. 19. Through anterior part of trunk.

Fig. 20. Through same region as fig. 19, shewing a groove (_x_) in the
epiblast, probably artificially formed in the process of hardening.

Fig. 21. Through anterior part of tail region, shewing partial fusion
of layers.

Fig. 22. Through posterior part of tail region, shewing more complete
fusion of layers than fig. 21.

Figs. 23-25. Transverse sections of an embryo on the fifth day after impregnation.

Fig. 23. Through fore-brain and optic vesicles.

Fig. 24. Through hind-brain and auditory pits.

Fig. 25. Through anterior part of trunk.

Figs. 26-27. Transverse sections of the head of an embryo on the sixth day after impregnation.

Fig. 26. Through fore-brain and optic vesicles.

Fig. 27. Through hind-brain and auditory pits.

PLATE 36.

Figs. 28-29. Transverse sections of the trunk of an embryo on the sixth day after impregnation.

Fig. 28. Through anterior part of trunk (from a slightly older embryo
than the other sections of this stage).

Fig. 29. Slightly posterior to fig. 28, shewing formation of segmental
duct as a fold of the somatic mesoblast.

Fig. 30. Longitudinal horizontal section of embryo on the sixth day after impregnation, passing through the mesoblastic somites, notochord, and medullary canal.

Figs. 31-34. Transverse sections through an embryo on the seventh day after impregnation.

Fig. 31. Through anterior part of trunk.

Fig. 32. Through the trunk somewhat behind fig. 31.

Fig. 33. Through tail region.

Fig. 34. Further back than fig. 33, shewing constriction of tail from
the yolk.

Figs. 35-37. Transverse sections through an embryo on the eighth day after impregnation.

Fig. 35. Through fore-brain and optic vesicles.

Fig. 36. Through hind-brain, shewing closed auditory pits, &c.

Fig. 37. Through anterior part of trunk.

Fig. 38. Section through tail of an embryo on the ninth day after
impregnation.

PLATE 37.

Fig. 39. Section through the olfactory involution and part of fore-brain of a larva on the ninth day after impregnation, shewing olfactory nerve.

Fig. 40. Section through the anterior part of the head of the same larva, shewing pituitary involution.

Figs. 41-43. Transverse sections through an embryo on the eleventh day after impregnation.

Fig. 41. Through fore-part of head, shewing the pituitary body still
connected with the oral epithelium.

Fig. 42. Slightly further back than fig. 41, shewing the pituitary
body constricted off from the oral epithelium.

Fig. 43. Slightly posterior to fig. 42, to shew olfactory involution,
eye, and hyomandibular cleft.

Fig. 44. Longitudinal section of the head of an embryo of 15 millims. in length, a few days after hatching, shewing the structure of the brain.

Fig. 45. Longitudinal section of the head of an embryo, about five weeks after hatching, 26 millims. in length, shewing the structure of the brain. In the front part of the brain the section passes slightly to one side of the median line.

Figs. 46A to 46G. Transverse sections through the brain of an embryo 25 millims. in length, about a month after hatching.

Fig. 46A. Through anterior lobes of cerebrum.

Fig. 46B. Through posterior lobes of cerebrum.

Fig. 46C. Through thalamencephalon.

Fig. 46D. Through optic thalami and optic chiasma.

Fig. 46E. Through optic lobes and infundibulum.

Fig. 46F. Through optic lobes and cerebellum.

Fig. 46G. Through optic lobes and cerebellum, slightly in front of
fig. 46F.

PLATE 38.

Figs. 47A, B, C. Figures of adult brain.

Fig. 47A. From the side.

Fig. 47B. From above.

Fig. 47C. From below.

Fig. 48. Longitudinal vertical section through the eye of an embryo, about a week after hatching, shewing the vascular membrane surrounding the vitreous humour.

Fig. 49. Diagram shewing the arrangement of the vessels in the vascular membrane of the vitreous humour of adult eye.

Fig. 50. Capillaries of the same vascular membrane.

Fig. 51. Transverse section through anterior part of trunk of an embryo on the ninth day after impregnation, shewing the pronephros and pronephric chamber.

Fig. 52. Transverse section through the region of the stomach of an embryo 15 millims. in length, shortly after hatching, to shew the glomerulus and peritoneal funnel of pronephros.

Fig. 53. Transverse section through posterior part of the body of an embryo, about a month after hatching, shewing the structure of the mesonephros, the spiral valve, &c.

PLATE 39.

Figs. 54, 55, 56, and 57 are a series of transverse sections through the genital ridge and mesonephros of one side from a larva of 11 centims.

Fig. 54. Section of the lymphatic organ which lies in front of the
mesonephros.

Fig. 55. Section near the anterior end of the mesonephros, where the
genital sack is completely formed.

Fig. 56. Section somewhat further back, shewing the mode of formation
of the genital sack.

Fig. 57. Section posterior to the above, the formation of the genital
sack not having commenced, and the genital ridge with primitive
germinal cells projecting freely into the body-cavity.

Fig. 58A. View of the testis, mesorchium, and duct of the kidney of the left side of an adult male example of _Lepidosteus_, 60 centims. in length, shewing the vasa efferentia and the longitudinal canal at the base of the mesorchium. The kidney ducts have been cut open posteriorly to shew the structure of the interior.

Fig. 58B. Inner aspect of the posterior lobe of the testis from the same example, to shew the vasa efferentia forming a network on the face of the testis.

Figs. 59A and B. Two sections shewing the structure and relations of the efferent ducts of the testis in the same example.

Fig. 59A. Section through the inner aspect of a portion of the testis
and mesorchium, to shew the network of the vasa efferentia (_nve_)
becoming continuous with the seminal tubes (_st_). The granular matter
nearly filling the vasa efferentia and the seminal tubes represent the
spermatozoa.

Fig. 59B. Section through part of the kidney and its duct and the
longitudinal canal (_lc_) at the base of the mesorchium. Canals (_sc_)
are seen passing off from the latter, which enter the kidney and join
the uriniferous tubuli. Some of the latter (as well as the seminal
tubes) are seen to be filled with granular matter, which we believe to
be the remains of spermatozoa.

Fig. 60. Diagram of the urinogenital organs of the left side of an adult female example of _Lepidosteus_ 100 centims. in length. This figure shews the oviduct (_od_) continuous with the investment of the ovary, opening at _od´_ into the dilated part of the kidney duct (segmental duct). It also shews the segmental duct and the junction of the latter with its fellow of the right side to form the so-called bladder, this part being represented as cut open. The kidney (_k_) and lymphatic organ (_ly_) in front of it are also shewn.

PLATE 40.

Fig. 61. Transverse section through the developing pancreas (_p_) of a larva 11 millims. in length.

Fig. 62. Longitudinal section through portions of the stomach, liver, and duodenum of an embryo about a month after hatching, to shew the relations of the pancreas (_p_) to the surrounding parts.

Fig. 63. External view of portions of the liver, stomach, duodenum, &c., of a young Fish, 11 centims. in length, to shew the pancreas (_p_).

Fig. 64. Transverse section through the anterior part of the trunk of an embryo, about a month after hatching, shewing the connection of the air-bladder with the throat (_ab´_).

Fig. 65. Transverse section through the same embryo as fig. 64 further back, shewing the posterior part of the air-bladder (_ab_).

Fig. 66. Viscera of an adult female, 100 centims. in length, shewing the alimentary canal with its appended glands in natural position, and the air-bladder with its aperture into the throat (_ab´_). The proximal part of the duodenum and the terminal part of the intestine are represented as cut open, the former to shew the pyloric valve and the apertures of the pyloric cæca and bile duct, and the latter to shew the spiral valve.

This figure was drawn for us by Professor A. C. Haddon.

PLATE 41.

Fig. 67. Transverse section through the tail of an advanced larva, shewing the neural and hæmal processes, the independently developed interneural and interhæmal elements (_is_), and the commencing dermal fin-rays (_df_).

Fig. 68. Side view of the tail of a larva, 21 minims. in length, dissected so as to shew the structure of the skeleton.

Fig. 69. Longitudinal horizontal section through the vertebral column of a larva, 5.5 centims. in length, on the level of the hæmal arches, shewing the intervertebral rings of cartilage continuous with the arches, the vertebral constriction of the notochord, &c.

Figs. 70 and 71. Transverse sections through the vertebral column of a larva of 5.5 centims. The red represents bone, and the blue cartilage.

Fig. 70. Through the vertebral region, shewing the neural and hæmal
arches, the notochordal sheath, &c.

Fig. 71. Through the intervertebral region, shewing the intervertebral
cartilage.

Figs. 72 and 73. Transverse sections through the trunk of a larva of 5.5 centims. to shew the structure of the ribs and hæmal arches.

Fig. 72. Through the anterior part of the trunk.

Fig. 73. Through the posterior part of the trunk.

PLATE 42.

Figs. 74-76. Transverse sections through the trunk of the same larva as figs. 72 and 73.

Fig. 74. Through the posterior part of the trunk (rather further back
than fig. 73).

Fig. 75. Through the anterior part of the tail.

Fig. 76. Rather further back than fig. 75.

Fig. 77. Longitudinal horizontal section through the vertebral column of a larva of 11 centims., passing through the level of the hæmal arches, and shewing the intervertebral constriction of the notochord, the ossification of the cartilage, &c.

Fig. 78. Transverse section through a vertebral region of the vertebral column of a larva 11 centims. in length.

Fig. 79. Transverse section through an intervertebral region of the same larva as fig. 78.

Fig. 80. Side view of two trunk vertebræ of an adult _Lepidosteus_.

Fig. 81. Front view of a trunk vertebra of adult.

In figures 80 and 81 the red does not represent bone as in the other figures, but simply the ligamentum longitudinale superius.

XXIII. ON THE NATURE OF THE ORGAN IN ADULT TELEOSTEANS AND
GANOIDS, WHICH IS USUALLY REGARDED AS THE HEAD-KIDNEY
OR PRONEPHROS[555].

Footnote 555: From the _Quarterly Journal of Microscopical
Science_, Vol. XXII., 1882.

While working at the anatomy of _Lepidosteus_ I was led to doubt the accuracy of the accepted accounts of the anterior part of the kidneys in this[556] and in allied species of Fishes. In order to test my doubts I first examined the structure of the kidneys in the Sturgeon (Acipenser), of which I fortunately had a well-preserved specimen.

Footnote 556: I am about to publish, in conjunction with Mr
Parker, a full account of the anatomy and development of
Lepidosteus [No. XXII. of this edition], and shall therefore in
this paper make no further allusion to it.

The bodies usually described as the kidneys consist of two elongated bands, attached to the dorsal wall of the abdomen, and extending for the greater part of the length of the abdominal cavity. In front each of these bands first becomes considerably narrowed, and then expands and terminates in a great dilatation, which is usually called the head-kidney. Along the outer border of the hinder part of each kidney is placed a wide ureter, which ends suddenly in the narrow part of the body, some little way behind the head-kidney. To the naked eye there is no distinction in structure between the part of the so-called kidney in front of the ureter and that in the region of the ureter. Any section through the kidney in the region of the ureter suffices to shew that in this part the kidney is really formed of uriniferous tubuli with numerous Malpighian bodies. Just in front, however, of the point where the ureter ends the true kidney substance rapidly thins out, and its place is taken by a peculiar tissue formed of a trabecular work filled with cells, which I shall in future call lymphatic tissue. _Thus the whole of that part of the apparent kidney in front of the ureter, including the whole of the so-called head-kidney, is simply a great mass of lymphatic tissue, and does not contain a single uriniferous tubule or Malpighian body._

The difference in structure between the anterior and posterior parts of the so-called kidney, although not alluded to in most modern works on the kidneys, appears to have been known to Stannius, at least I so interpret a note of his in the second edition of his _Comparative Anatomy_, p. 263, where he describes the kidney of the Sturgeon as being composed of two separate parts, viz. a spongy vascular substance (no doubt the so-called head-kidney) and a true secretory substance.

After arriving at the above results with reference to the Sturgeon I proceeded to the examination of the structure of the so-called head-kidney in Teleostei.

I have as yet only examined four forms, viz. the Pike (_Esox lucius_), the Smelt (_Osmerus eperlanus_), the Eel (_Anguilla anguilla_), and the Angler (_Lophius piscatorius_).

The external features of the apparent kidney of the Pike have been accurately described by Hyrtl[557]. He says: "The kidneys extend from the second trunk vertebra to the end of the abdominal cavity. Their anterior extremities, which have the form of transversely placed coffee beans, are united together, and lie on the anterior end of the swimming bladder. The continuation of the kidney backwards forms two small bands, separated from each other by the whole breadth of the vertebral column. They gradually, however, increase in breadth, so that about the middle of the vertebral column they unite together and form a single symmetrical, keel-shaped body," &c.

Footnote 557: "Das Uropoëtische System der Knochenfische,"
_Sitz. d. Wien. Akad._, 1830.

The Pike I examined was a large specimen of about 58 centimètres in length, and with an apparent kidney of about 25-1/2 centimètres. The relations of lymphatic tissue and kidney tissue were much as in the Sturgeon. The whole of the anterior swelling, forming the so-called head-kidney, together with a considerable portion of the part immediately behind, forming not far short of half the whole length of the apparent kidney, was entirely formed of lymphatic tissue. The posterior part of the kidney was composed of true kidney substance, but even at 16 centimètres from the front end of the kidney the lymphatic tissue formed a large portion of the whole.