Chapter XIV: Introduction: To Part III (3)

I am indebted to Mr. F. H. Gravely, Assistant Superintendent in the Indian Museum, for an interesting note regarding the food of _Plumatella_. His observations, which were made in Northamptonshire, were unfortunately interrupted at a critical moment, but I have reproduced them with his consent in order that other observers may investigate the phenomena he saw. Mr. Gravely noted that a small green flagellate which was abundant in water in which _Plumatella repens_ was growing luxuriantly, was swallowed by the polypides, and that if the polyparium was kept in a shallow dish of water, living flagellata of the same species congregated in a little pile under the anus of each polypide. His preparations show very clearly that the flagellates were passing through the alimentary canal without apparent change, but the method of preservation does not permit the retractile granules, which were present in large numbers in the cell-substance of the flagellates, to be displayed and it is possible that these granules had disappeared from those flagellates which are present in the recta of his specimens. It is clear, therefore, either that certain flagellates must pass through the alimentary canal of _Plumatella_ unchanged, or that the polyzoon must have the power of absorbing the stored food material the flagellates contain without doing them any other injury.

The free statoblasts of _Plumatella_ are as a rule set free before the cells they contain become differentiated, and float on the surface of the water for some time before they germinate; but occasionally a small polypide is formed inside the capsule while it is still in its parent zooecium. I have, however, seen only one instance of this premature development, in a single statoblast contained in a small zoarium of _P. fruticosa_ found in Lower Burma in March. The fixed statoblasts usually remain fixed to the support of the zoarium, even when their parent-zooecium decays, and germinate _in situ_.

The larva (fig. 40 C, p. 207) that originates from the egg of _Plumatella_ is a minute pear-shaped, bladder-like body covered externally with fine vibratile threads (cilia) and having a pore at the narrow end. At the period at which it is set free from the parent zooecium it already contains a fully formed polypide or pair of polypides with the tentacles directed towards the narrow end. After a brief period of active life, during which it moves through the water by means of its cilia, it settles down on its broad end, which becomes adhesive; the polypide or pair of polypides is everted through the pore at the narrow end, the whole of this end is turned inside out, and a fresh polyparium is rapidly formed by budding.

29. Plumatella fruticosa, _Allman_. (Plate III, fig. 1; plate IV, fig. 4; plate V, fig. 1.)

_Plumatella fruticosa_, Allman, Ann. Nat. Hist. xiii, p. 331
(1844).

_Plumatella repens_, van Beneden (? _nec_ Linné), Mém. Acad.
Roy. Belg. 1847, p. 21, pl. i, figs. 1-4.

_Plumatella fruticosa_, Johnston, Brit. Zooph. (ed. 2), p.
404 (1847).

_Plumatella coralloides_, Allman, Rep. Brit. Assoc. 1850, p.
335.

_Plumatella stricta_, _id._, Mon. Fresh-Water Polyzoa, p.
99, fig. 14 (1857).

_Plumatella fruticosa_, _id._, _ibid._ p. 102, pl. vi, figs.
3-5.

_Plumatella coralloides_, _id._, _ibid._ p. 103, pl. vii,
figs. 1-4.

_Plumatella repens_ and _P. stricta_, Carter, Ann. Nat.
Hist. (3) iii, p. 341 (1859).

_Plumatella lucifuga_, Jullien (_partim_), Bull. Soc. zool.
France, x, p. 114 (1885).

_Plumatella princeps_ var. _fruticosa_, Kraepelin, Deutsch.
Süsswasserbryozoen, i, p. 120, pl. vii, fig. 148 (1887).

_Plumatella fruticosa_, Braem, Unter. ii. Bryozoen des
süssen Wassers, p. 9, pl. i, fig. 15 (Bibl. Zool. ii)
(1890).

_Plumatella repens_, Annandale, J. As. Soc. Bengal (new
series) iii, 1907, p. 88.

_Plumatella emarginata_, Loppens (_partim_), Ann. Biol.
lacustre, iii, p. 161 (1908).

_Plumatella fruticosa_, Annandale, Rec. Ind. Mus. v, p. 45
(1910).

_Zoarium._ The zoarium in the typical form has a loose appearance due to the fact that the branches are far apart and the ectocyst by no means rigid. When young the zoarium is adherent, but in well-grown polyparia vertical branches, often an inch or more in length, are freely produced. As a rule they have not the strength to stand upright if removed from the water. Branching is ordinarily lateral and as a rule occurs chiefly on one side of a main branch or trunk. In certain circumstances upright zooecia are pressed together and reach a great length without branching, and in this form (_P. coralloides_, Allman) daughter-zooecia are often produced at the tip of an elongated mother-zooecium in fan-like formation. A depauperated form (_P. stricta_, Allman), occurs in which the vertical branches are absent or very short. In all forms internal partitions are numerous and stout.

_Zooecia._ The zooecia are cylindrical and bear a simple keel on their dorsal surface. They are never emarginate or furrowed. In the typical form their diameter is more than half a millimetre, and they are always of considerable length. The ectocyst is thin and never very rigid or deeply pigmented, the colour usually being an almost uniform pale pinkish brown and fading little towards the tip of the zooecium.

_Statoblasts._ Both free and stationary statoblasts are formed, but the latter are rare and do not always adhere. They resemble the free statoblasts in general form but have a solid margin instead of a swim-ring and are often minutely serrated round the edge. The free statoblasts are at least considerably, sometimes very elongate; in all zoaria it is possible to find specimens that are more than twice as long as broad. The capsule is relatively large and resembles the swim-ring in outline, so that the free portion of the latter is not much narrower at the sides than at the ends. The sides are distinctly convex and the ends rounded; the swim-ring encroaches little on the surface of the capsule.

_Polypide._ The tentacles number between 40 and 50 and are not festooned at the base. The stomach is slender and elongate.

TYPE not in existence.

SYSTEMATIC REMARKS.--_P. fruticosa_ is closely allied to _P. repens_ (European and N. American) but always has much longer statoblasts. Three phases of the species may be distinguished as follows:--

A. (_Forma typica_). Zooecia stout in form, not greatly
elongate; free branches produced in profusion.

B. (_P. stricta_, Allman, _P. repens_, van Beneden). Zooecia
slender; free branches absent or consisting of two or three
zooecia only.

C. (_P. coralloides_, Allman). Vertical zooecia pressed
together and greatly elongated.

Indian specimens of the typical form agree well with German specimens labelled by Prof. Kraepelin _P. princeps_ var. _fruticosa_, and specimens of the _coralloides_ phase could hardly be distinguished from similar specimens from Scotland.

GEOGRAPHICAL DISTRIBUTION.--_P. fruticosa_ is widely distributed in Europe and probably in N. America. I have seen Indian specimens from the Punjab (Lahore, _Stephenson_), from Bombay, from Travancore, from Calcutta and other places in the Ganges delta, from Rajshahi (Rampur Bhoolia) on the R. Ganges, from Kurseong in the E. Himalayas (alt. 4,500 feet), and from Kawkareik in Tenasserim. Statoblasts found on the surface of a pond near Simla in the W. Himalayas (alt. _ca._ 8,000 feet), probably belong to this species.

BIOLOGY.--Allman states that in England _P. fruticosa_ is fond of still and slowly-running water. The typical form and the _coralloides_ phase grow abundantly in the Calcutta tanks, the former often attaining an extraordinary luxuriance. I have found the var. _stricta_ only in water in which there was reason to suspect a lack of minute life (and therefore of food), viz. in Shasthancottah Lake in Travancore, in a swamp in Lower Burma, and in a small jungle stream near the base of the Western Ghats in Travancore. The species is the only one that I have seen in running water in India, and the specimens obtained in the jungle stream in Travancore are the only specimens I have taken in these circumstances. _P. fruticosa_ always grows near the surface or near the edge of water; it is found attached to the stems of bulrushes and other aquatic plants, to floating seeds and logs and (rarely) to stones and bricks. So far as my experience goes it is only found, at any rate in Calcutta, in the cold weather and does not make its appearance earlier than October.

The form Allman called _P. coralloides_ was found by him, "attached to floating logs of wood, together with _P. repens_ and _Cordylophora lacustris_, and generally immersed in masses of _Spongilla fluviatilis_." I have always found it immersed in sponges (_S. lacustris_, _S. alba_, _S. carteri_, and _S. crassissima_), except when the sponge in which it had been immersed had decayed. Indeed, the peculiar form it has assumed appears to be directly due to the pressure of the growing sponge exerted on the zooecia, for it is often possible to find a zoarium that has been partially overgrown by a sponge and has retained its typical form so long as it was free but has assumed the _coralloides_ form where immersed.[BI] In Shasthancottah Lake, Travancore, I found specimens of the _stricta_ phase embedded in the gelatinous mass formed by a social rotifer and to some extent assimilated to the _coralloides_ form.

[Footnote BI: Braem (_op. cit._, p. 3, pl. i, fig. 1), has
described and figured under the name _P. fungosa_ var.
_coralloides_, Allman, a dense form that somewhat resembles
this phase of _P. fruticosa_ but has become compacted
without external pressure. It is, however, probably a form
of _P. repens_ rather than _P. fungosa_ and differs in its
broad statoblasts from any form of _P. fruticosa_. I have
examined specimens of the same form from England.]

30. Plumatella emarginata, _Allman_. (Plate III, fig. 2; plate IV, figs. 1, 1 _a._)

_Plumatella emarginata_, Allman, Ann. Nat. Hist. xiii, p.
330 (1844).

_Plumatella emarginata_, Johnston, Brit. Zooph. (ed. 2), p.
404 (1847).

_Alcyonella benedeni_, Allman, Mon. Fresh-Water Polyzoa, p.
89, pl. iv, figs. 5-11 (1857).

_Plumatella emarginata_, _id._, _ibid._ p. 104, pl. vii,
figs. 5-10.

_Plumatella lucifuga_, Jullien, Bull. Soc. zool. France, x,
figs. 89, 90, p. 114 (1885).

_Plumatella princeps_ var. _emarginata_, Kraepelin
(_partim_), Deutsch. Süsswasserbryoz. p. 120, pl. iv, fig.
108, pl. v, fig. 123 (1887).

_Plumatella emarginata_, Braem, Unter. ii. Bryoz. süssen
Wassers, p. 9, pl. i, figs. 12, 14 (Bibl. Zool. ii) (1890).

_Plumatella emarginata_, Annandale (_partim_), J. As. Soc.
Bengal, (new series) iii, 1907, p. 89.

_Plumatella princeps_, Loppens (_partim_), Ann. Biol.
lacustre, iii, p. 162, fig. 7 (1908).

_Plumatella emarginata_, Annandale, Rec. Ind. Mus. v, p. 47
(1910).

_Zoarium._ The zoarium often covers a considerable area on flat surfaces and is sometimes entirely recumbent. More usually, however, the younger part is vertical. In either case the branching is practically dichotomous, two young zooecia arising almost simultaneously at the tip of a mother-zooecium and diverging from one another at a small angle. When the zoarium becomes vertical, rigid branches of as much as an inch in length are sometimes produced in this way and, arising parallel to one another, are pressed together to form an almost solid mass (=_Alcyonella benedeni_, Allman). In such cases the basal zooecium or at any rate the basal part of each upright branch is considerably elongated. In recumbent zooecia the main branches often radiate outwards from a common centre.

_Zooecia._ The zooecia are of almost equal width throughout, slender, and moderately elongate when recumbent. Their ectocyst is stiff; they are emarginate at the tip and more or less distinctly furrowed on the dorsal surface, the keel in which the furrow runs not being prominent. The orifice is often on the dorsal surface even in upright branches. Each zooecium is of a dark brown or almost black colour for the greater part of its length but has a conspicuous white tip which is extended down the dorsal surface in the form of a triangle, its limits being rather more extensive than and parallel to those of the emargination.

_Statoblast._ The majority of the free statoblasts are elongate and truncate or subtruncate at the extremities, the sides being as a rule straight and parallel. In every polyparium specimens will be found that are between twice and thrice as long as broad. The capsule is, however, relatively much broader than the swim-ring, often being nearly circular, and there is therefore at either end a considerable extent of free air-cells, while the extent of these cells at the sides of the capsule is small. The air-cells cover a considerable part of the dorsal surface of the capsule. Fixed statoblasts are usually found in old colonies, especially at the approach of the hot weather. They have an oval form and are surrounded by a membranous margin on which traces of reticulation can often be detected. As a rule statoblasts of both types are produced in considerable but not in excessive numbers.

_Polypide._ There are about 40 tentacles, the velum at the base of which extends upwards for a considerable distance without being festooned. The stomach is elongate and slender and narrowly rounded at the base.

The method of branching, the coloration of the zooecia and the form of the free statoblast are all characteristic. Luxuriant or closely compressed zoaria of _P. diffusa_ often bear a superficial resemblance to those of _P. emarginata_, but the resemblance disappears if they are carefully dissected out. Indian specimens of _P. emarginata_ agree closely with European ones.

GEOGRAPHICAL DISTRIBUTION.--_P. emarginata_ is a common species in Europe, N. America, and southern Asia and probably also occurs in Africa and Australia. I have examined specimens from Calcutta, Rangoon, and Mandalay in Indian territory, and also from Jalor in the Patani States (Malay Peninsula) and the Talé Noi, Lakon Sitamarat, Lower Siam. Gemmules found by Apstein (Zool. Jahrb. (Syst.) xxv, 1907, p. 201) in plankton from the Colombo lake may belong to this species or to any of the others included by Kraepelin in his _P. princeps_.

BIOLOGY.--In Ireland Allan found _P. emarginata_ in streams and rivulets, but it also occurs in European lakes. In India I have only found it in ponds. It prefers to adhere to the surface of stones or bricks, but when these are not available is found on the stems of water-plants. In the latter position the form called _Alcyonella benedeni_ by Allman is usually produced, owing to the fact that the upright branches are crowded together through lack of space, very much in the same way (although owing to a different cause) as those of _P. fruticosa_ are crowded together in the _coralloides_ phase, to which the _benedeni_ phase of _P. emarginata_ is in many respects analogous.

Although it is essentially a cold-weather species in Calcutta, _P. emarginata_ is sometimes found in a living condition during the "rains." Zoaria examined at this season, however, contains few living polypides, the majority of the zooecia having rotted away and left fixed statoblasts only to mark their former position.

31. Plumatella javanica, _Kraepelin_.

_Plumatella javanica_, Kraepelin, Mitt. Nat. Mus. Hamb.
xxiii, p. 143, figs. 1-3 (1903).

_Plumatella emarginata_ var. _javanica_, Loppens, Ann. Biol.
lacustre, iii, p. 162 (1908).

_Plumatella javanica_, Annandale, Rec. Ind. Mus. v, p. 50
(1910).

_Plumatella allmani_ var. _dumortieri_, _id._ (_partim_)
(_nec_ Allman), _ibid._ p. 49.

This species is related to _P. emarginata_, from which it may be distinguished by the following characters:--

_Zoarium._ The zoarium is always entirely recumbent and branches sparingly; its method of branching does not approach the dichotomous type but is lateral and irregular. Linear series of zooecia without lateral branches are often formed.

_Zooecia._ The zooecia are slender and often very long; they are strongly emarginate and furrowed, and the keel that contains the furrow is conspicuous. The ectocyst is hyaline and as a rule absolutely colourless.

_Statoblasts._ The free statoblasts are variable in length, sometimes distinctly elongate, sometimes elongate only to a moderate degree; they are rounded at the extremities and have the sides slightly or distinctly convex outwards. The capsule is relatively large, and the free portion of the swim-ring is not much broader at the ends than at the sides. The fixed statoblasts are elongate and surrounded by an irregularly shaped chitinous membrane, which is often of considerable extent. The whole of the dorsal surface is covered with what appear to be rudimentary air-spaces some of which even contain air.

The transparent glassy ectocyst and strong furrowed keel of this species are very characteristic, but the former character is apt to be obscured by staining due to external causes, especially when the zoarium is attached to dead wood. The shape of the free statoblasts is too variable to be regarded as a good diagnostic character, but the fixed statoblasts, when they are to be found, are very characteristic in appearance. _P. javanica_ appears to be closely related to Allman's _P. dumortieri_, with which stained zoaria are apt to be confused. The character of the ectocyst is, however, different, and the free part of the swim-ring is distinctly narrower at the sides of the free statoblasts. Dr. Kraepelin has been kind enough to send me one of the types.

TYPES in the Hamburg and Indian Museums.

GEOGRAPHICAL DISTRIBUTION.--Java, Penang, India. Indian localities are:--BENGAL, Calcutta; Berhampore, Murshidabad; R. Jharai, Siripur, Saran district, Tirhut: E. HIMALAYAS, Kurseong, Darjiling district (alt. 4,500 feet): MADRAS PRESIDENCY, canal near Srayikaad, Travancore. Mr. C. W. Beebe has recently sent me a specimen taken by him in the Botanical Gardens at Penang.

BIOLOGY.--Very little is known about the biology of this species. Kraepelin took it in Java on the leaves of water-lilies. It is not uncommon during the cold weather in the Calcutta Zoological Gardens on floating seeds and sticks and on the stems of bulrushes; in Travancore I took it in November on the submerged leaves of _Pandani_ growing at the edge of a canal of slightly brackish water. Mr. Hodgart, the collector of the Indian Museum, found it in the R. Jharai on the stems of water-plants at a time of flood in the "rains." In Calcutta it is often found entangled with _P. fruticosa_ and _P. emarginata_.

32. Plumatella diffusa, _Leidy_. (Plate IV, fig. 2.)

_Plumatella diffusa_, Leidy, P. Ac. Philad. v, p. 261
(1852).

_Plumatella diffusa_, Allman, Mon. Fresh-Water Polyzoa, p.
105 (1857).

_Plumatella diffusa_, Hyatt, Comm. Essex Inst. iv, pl. viii,
figs. 11, 12 (1866).

_Plumatella diffusa_, _id._, _ibid._ v, p. 107, fig. 12
(1868).

_Plumatella repens_, Jullien, Bull. Soc. zool. France, x,
fig. 37 (_lapsus_ for 73), p. 110 (1885).

_Plumatella diffusa_, _id._, _ibid._ figs. 155, 157, pp.
130, 131.

_Plumatella allmani_ var. _diffusa_, Annandale, Rec. Ind.
Mus. v, p. 49 (1910).

_Zoarium._ The zoarium often covers a considerable area on flat surfaces and is sometimes found crowded together on the stems of plants. In the latter case the arrangement of the main branches is distinctly radiate. Upright branches occur rarely and never consist of more than three zooecia. The characteristic method of branching is best represented by the following diagram:--

The partitions are stout and numerous.

_Zooecia._ The great majority of the zooecia in each zoarium are distinctly L-shaped, the long limb being usually adherent. The vital organs of the polypide are contained in the vertical limb, while the horizontal one, in mature polyparia, is packed full of free statoblasts. The zooecia are cylindrical and as a rule obscurely emarginate and furrowed. The ectocyst is stiff; it is never deeply pigmented but is usually of a transparent horn-colour at the base of each zooecium and colourless at the tip, the contrast between the two portions never being very strong. The basal portion is rough on the surface, the distal portion smooth.

_Statoblasts._ Free statoblasts are produced in very great profusion and fixed statoblasts are also to be found as a rule. The latter resemble those of _P. emarginata_. The free statoblasts are never very large or relatively broad, but they vary considerably as regards size and outline. The capsule is large, the sides convex outwards and the extremity more or less broadly rounded. The air-cells are unusually large and extend over a great part of the dorsal surface of the statoblast.

_Polypide._ The polypide is shorter and stouter than that of _P. emarginata_ and as a rule has fewer tentacles.

The most characteristic feature of this species is the form of the zooecia, which differ greatly from those of any other Indian species but _P. allmani_. In the latter they are distinctly "keg-shaped" (_i. e._, constricted at the base and swollen in the middle), and the zoarium never spreads out over large surfaces in the way in which that of _P. diffusa_ does.

TYPE--? in the Philadelphia Academy of Sciences.

GEOGRAPHICAL DISTRIBUTION.--This species was originally described from North America (in which it is apparently common) and occurs also in Europe. I have seen Indian specimens from the following localities:--BENGAL, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia): E. HIMALAYAS, Gangtok, Native Sikhim (alt. 6,150 feet) (_Kirkpatrick_, _Stewart_): PUNJAB, Lahore (_Stephenson_).

BIOLOGY.--_P. diffusa_ in Lower Bengal is a cold-weather species. It is remarkable for the enormous number of gemmules it produces and is usually found either on floating objects such as the stems of certain water-plants, or on stones or bricks at the edge of ponds.

33. Plumatella allmani, _Hancock_. (Plate IV, figs. 3, 3 _a_.)

_Plumatella allmani_, Hancock, Ann. Nat. Hist. (2) v, p.
200, pl. v, fig. 3-4, pl. iii, fig. 2-3 (1850).

_Plumatella allmani_, Allman, Mon. Fresh-Water Polyzoa, p.
106, fig. 16 (1857).

_Plumatella elegans_, _id._, _ibid._ p. 107, pl. viii, figs.
6-10.

_Plumatella lucifuga_ ("forme rampante") Jullien, Bull. Soc.
zool. France, x, p. 114 (1885).

This species is closely allied to _P. diffusa_, from which it differs in the following characters:--

(1) The zoarium never covers a large area and as a rule
grows sparingly and mainly in two directions.

(2) The zooecia are more irregular in shape, not so
distinctly elbowed, smaller; they have a much more
prominently keeled ridge. The great majority of them are
constricted at the base and taper towards the orifice. In
young zoaria they are almost colourless but in older ones
there is a band of not very dense pigment round the base of
the vertical limb.

(3) The free statoblasts are comparatively large and usually
show a tendency to taper at the extremities, often being
almost rhomboidal in form. The swim-ring does not extend so
far over the dorsal surface as it does in those of _P.
diffusa_; the "cells" of which it is composed are small.

TYPE not in existence.

I have seen every gradation between this form and Allman's _P. elegans_.

GEOGRAPHICAL DISTRIBUTION.--_P. allmani_ is apparently a rare species to which there are few references in literature. It was originally described from England and is stated by Jullien to occur in France. I have found specimens only in the lake Bhim Tal (alt. 4,500 feet) in the W. Himalayas.

BIOLOGY.--The original specimens were found by Hancock on stones. My own were growing on the leaves of water-plants, usually on the under side. When the zooecia were forced to stretch across from one leaflet to another they assumed the sinuous form characteristic of Allman's _P. elegans_.

34. Plumatella tanganyikæ, _Rousselet_.

_Plumatella tanganyikæ_, Rousselet, Proc. Zool. Soc. London,
1907 (i), p. 252, pl. xiv, figs. 1-4.

_Plumatella bombayensis_, Annandale, Rec. Ind. Mus. ii, p.
169, figs. 1, 2 (1908).

_Plumatella bombayensis_, _id._, _ibid._ v, p. 51 (1910).

_Zoarium._ The whole colony is recumbent but branches freely and at short intervals in a horizontal plane, so that the zooecia become crowded together and the branches sometimes overlap one another. The zoarium often covers a considerable area, but growth seems to be mainly in two directions. When growing on the stems of water-plants the branches are often parallel and closely pressed together but remain recumbent in this position. A stout membrane sometimes extends between branches and individual zooecia.

_Zooecia._ The walls of the zooecia are thick, stiff, and more or less darkly but not opaquely pigmented; the external surface, although not very smooth, is always clean. The two most noteworthy characters of the zooecia are (i) their truncated appearance when the polypide is retracted, and (ii) the conspicuous, although often irregular external annulation of their walls. The tip of each zooecium, owing to the fact that the invaginated part of the ectocyst is soft and sharply separated from the stiffened wall of the tube, terminates abruptly and is not rounded off gradually as is the case in most species of the genus; sometimes it expands into a trumpet-like mouth. The annulation of the external surface is due to numerous thickened areas of the ectocyst which take the form of slender rings surrounding the zooecium; they are most conspicuous on its distal half. On the dorsal surface of the base of each zooecium there is a conspicuous furrowed keel, which, however, does not usually extend to the distal end; the latter is oval in cross-section. The zooecia are short and broad; their base is always recumbent, and, when the zoarium is attached to a stone or shell, often seems to be actually embedded in the support; the distal part turns upwards and is free, so that the aperture is terminal; the zooecia of the older parts of the zoarium exhibit the specific characters much more clearly than those at the growing points.

_Polypide._ The lophophore bears 20 to 30 tentacles, which are long and slender; the velum at their base extends up each tentacle in the form of a sharply pointed projection, but these projections do not extend for more than one-fifth of the length of the tentacles. Both the velum and the tentacular sheath bear numerous minute tubercles on the external surface. The base of the stomach is rounded, and the whole of the alimentary canal has a stout appearance.

A=outline of part of zoarium from a stone, × 16; B=outline of the tip of a single zooecium, × 70; C=free statoblast, × 70.]

_Statoblasts._ Both fixed and free statoblasts are produced, but not in very large numbers. The latter are broadly oval and are surrounded by a stout chitinous ring, which often possesses irregular membranous projections; the surface is smooth. The free statoblasts are small and moderately elongate, the maximum breadth as a rule measuring about 2/3 of the length; the capsule is relatively large and the ring of air-cells is not very much broader at the ends than at the sides; the dorsal surface of the central capsule is profusely tuberculate. The outline of the whole structure is often somewhat irregular.

In deference to Mr. Rousselet's opinion expressed in a letter I have hitherto regarded the Bombay form of this species as distinct from the African one, and there certainly is a great difference in the appearance of specimens taken on the lower surface of stones in Igatpuri Lake and of the types of _P. tanganyikæ_, one of which is now in the collection of the Indian Museum. The dark colour of the former, however, and their vigorous growth appear to be directly due to environment, for these characters disappear to a large extent in specimens growing on the stems of water-plants in the same lake. Indeed, such specimens are exactly intermediate between the form "_bombayensis_" and the typical form of the species. _P. tanganyikæ_ is closely allied to _P. philippinensis_, Kraepelin, from the island of Luzon, but the latter has a smooth and polished ectocyst devoid of annulations, and zooecia of a more elongate and regular form.

TYPES of the species in the British and Indian Museums, those of _P. bombayensis_ in the latter collection.

GEOGRAPHICAL DISTRIBUTION.--_P. tanganyikæ_ is only known as yet from L. Tanganyika in Central Africa and from Igatpuri in the Bombay Presidency.

BIOLOGY.--In both localities the zoaria were found in shallow water. In L. Tanganyika they were encrusting stones and shells, while at Igatpuri they were fixed for the most part to the lower surface of stones but were also found on the stems of water-plants. My specimens from the Bombay Presidency were taken, on two separate occasions, at the end of November. At that date the zoaria were already decaying and large blanks, marked out by fixed statoblasts, were often observed on the stones. Probably, therefore, the species flourishes during the "rains."

35. Plumatella punctata, _Hancock_. (Plate IV, fig. 5.)

_Plumatella punctata_, Hancock, Ann. Nat. Hist. (2) v, p. 200, pl. iii,
fig. 1, and pl. v, figs. 6, 7 (1850).

_Plumatella vesicularis_, Leidy, P. Ac. Philad. vii, p. 192 (1854).

_Plumatella vitrea_, Hyatt, Comm. Essex Inst. iv, pl. ix, figs. 1, 2
(1866).

_Plumatella punctata_, Allman, Mon. Fresh-Water Polyzoa, p. 100,
fig. 15 (1857).

_Plumatella vesicularis_, _id._, _ibid._ p. 101.

_Plumatella vitrea_, Hyatt, Proc. Essex Inst. v, p. 225,
figs. 18, 19 (1868).

_Plumatella vesicularis_, _id._, _ibid._ p. 225.

_Hyalinella vesicularis_, Jullien, Bull. Soc. zool. France,
x, p. 133, figs. 165-172 (1885).

_Hyalinella vitrea_, _id._, _ibid._ p. 134, figs. 173-179.

_Plumatella punctata_, Kraepelin, Deutsch.
Süsswasserbryozoen, i, p. 126, pl. iv, figs. 115, 116; pl.
v, figs. 124, 125; pl. vii, figs. 153, 154 (1887).

_Plumatella vesicularis_, Braem, Unters. ü. Bryozoen süssen
Wassers, p. 8, pl. i, fig. 8 (Bibl. Zool. ii) (1890).

_Hyalinella punctata_, Loppens, Ann. Biol. lacustre, iii, p.
163 (1908).

_Plumatella punctata_, Annandale, Rec. Ind. Mus. v, p. 52
(1910).

_Zoarium._ The zoarium is entirely recumbent and often appears to form an almost uniform flat layer instead of a dendritic body. Sometimes, however, it is distinctly linear, with lateral branches produced irregularly at considerable distances apart.

_Zooecia._ The zooecia differ from those of all other species in having a greatly swollen, soft ectocyst which can be transversely wrinkled all over the zooecium by the action of the muscles of the polypide and is distinctly contractile. It is mainly owing to the swollen and almost gelatinous nature of the ectocyst that the dendritic character of the zoarium is frequently concealed, for the method of branching is essentially the same as that of _P. diffusa_, although the zooecia are not so distinctly elbowed. The ectocyst is colourless or faintly tinted with brown; as a rule it is not quite hyaline and the external surface is minutely roughened or tuberculate. The zooecia are not emarginate or furrowed.

_Statoblasts._ Stationary statoblasts are not found. The free statoblasts are variable and often asymmetrical in outline, but the free portion of the swim-ring is always of nearly equal diameter all round the periphery and the capsule relatively large. Some of the statoblasts are always broad in comparison with their length.

_Polypide._ The polypide is comparatively short and stout. European specimens are said to have from 30 to 40 tentacles, but Indian specimens have only from 20 to 30.

Shrunken specimens of the less congested forms of this species closely resemble specimens of _P. repens_, but the statoblasts are more variable in shape and the ectocyst, even in such specimens, is thicker. Living or well-preserved specimens cannot be mistaken for those of any other species. Jullien regarded _P. punctata_ as the type of a distinct genus (_Hyalinella_) but included in _Plumatella_ at least one form (P. "_arethusa_") which probably belongs to this species. Kraepelin distinguishes as "varieties" two phases, a summer phase ("var. _prostrata_") and an autumn phase ("var. _densa_"). The former often forms linear series of considerable length with only an occasional side-branch, while in the autumn phase branching is so profuse and the branches are so closely pressed together that the zoarium comes to resemble a uniform gelatinous patch rather than a dendritic growth. A phase resembling the European autumn form is the commonest in Calcutta and I have also found one intermediate between this and Kraepelin's "var. _prostrata_," neither having any seasonal significance in India.

GEOGRAPHICAL DISTRIBUTION.--_P. punctata_ is widely distributed in Europe and N. America, but in the Oriental Region it has only been found in Calcutta and the neighbourhood.

BIOLOGY.--In this part of India _P. punctata_ flourishes both during the "rains" and in winter. I have found specimens in June and July and also in December and January. The majority of them were attached to bricks, but some were on the roots of duckweed, the stems of water-plants, and the tips of creepers falling into water. The species is often found together with _Stolella indica_ and also with other species of its own genus. It is most common, in the neighbourhood of Calcutta, in that part of the town which is near the Salt Lakes, and occurs in ponds the water of which is slightly brackish.

Genus 2. STOLELLA, _Annandale_.

_Stolella_, Annandale, Rec. Ind. Mus. iii, p. 279 (1909).

_Stolella_, _id._, _ibid._ v, p. 53 (1910).

TYPE, _Stolella indica_, Annandale.

_Zoarium_. The zoarium consists of groups of zooecia (or occasionally of single zooecia) joined together by an adherent rhizome. There is no gelatinous investment.

_Zooecia._ The adult zooecia resemble those of _Plumatella_ except in being sometimes more or less upright.

_Polypide_ and _Statoblasts._ The polypide and statoblasts resemble those of _Plumatella_. Fixed as well as free statoblasts occur.

This genus is closely allied to _Plumatella_, from which it is probably derived. The root-like tube from which the zooecia arise is formed by the great elongation of the basal part of a zooecium, and the zoaria closely resemble those of _P. punctata_, for it is not until several zooecia have been produced that the characteristic mode of growth becomes apparent.

_Stolella_ has only been found in India and is monotypic[BJ].

[Footnote BJ: But see p. 246 (addenda).]

36. Stolella indica, _Annandale_. (Plate V, figs. 3, 4.)

_Stolella indica_, Annandale, Rec. Ind. Mus. iii, p. 279, fig. (1909).

_Stolella indica_, _id._, _ibid._ v, p. 53 (1910).

_Zoarium._ The zoarium is adherent and linear, having neither lateral nor vertical branches.

_Zooecia._ The zooecia are short and slender, erect or nearly so, distinctly emarginate and furrowed. Their ectocyst is soft, colourless and transparent but minutely roughened on the surface.

_Polypide._ The tentacles number from 30 to 35 and are rather short and stout, sometimes being slightly expanded at the tips. The stomach is comparatively short and abruptly truncated posteriorly.

_Statoblasts._ Both free and fixed statoblasts are found, and both are variable in form, the latter varying in outline from the circular to the broadly oval. The free statoblasts resemble those of _Plumatella punctata_, but are sometimes rather more elongate.

TYPE in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--So far as we know, this species is confined to the Indo-Gangetic Plain. Major Walton found it at Bulandshahr in the United Provinces, and it is not uncommon in the neighbourhood of Calcutta.

BIOLOGY.--The zoaria of _S. indica_ are usually fixed to the roots of duckweed or to the stems of other plants. They are often found together with those of _P. punctata_. A slight infusion of brackish water into the ponds in which it lives does not seem to be inimical to this species, but I have found it in ponds in which nothing of the kind was possible. It flourishes during the "rains" and, to judge from specimens kept in an aquarium, is very short-lived. Major Walton found it growing over a zoarium of _Hislopia lacustris_.

Subfamily B. LOPHOPINÆ.

The zoaria of this subfamily are never dendritic but form gelatinous masses which, except in _Australella_, are cushion-shaped or sack-like. With the possible exception of _Australella_, they possess to a limited extent the power of moving along vertical or horizontal surfaces, but it is by no means clear how they do so (see p. 172). The statoblasts are remarkable for their large size, and it is noteworthy that _Australella_, which is intermediate in structure between the Plumatellinæ and the Lophopinæ, possesses statoblasts of intermediate size. The swim-ring is always well developed, and fixed statoblasts are unknown.

Only two genera (_Lophopodella_ and _Pectinatella_) have been definitely proved to occur in India, but a third (_Lophopus_[BK]) is stated to have been found in Madras. Should it be met with it will easily be recognized by the upright position of its polypides when their tentacles are expanded and by the fact that the statoblasts never bear marginal processes.

[Footnote BK: Only two species are known, _L. crystallinus_
(Pallas) from Europe and N. America, with oval statoblasts
that are produced and pointed at the two ends, and _L.
jheringi_, Meissner from Brazil, with irregularly polygonal
or nearly circular statoblasts.]

Genus 3. LOPHOPODELLA, _Rousselet_.

_Lophopodella_, Rousselet, Journ. Quek. Micr. Club (2) ix,
p. 45 (1904).

_Lophopodella_, Annandale, Rec. Ind. Mus. v, p. 54 (1910).

TYPE, _Pectinatella carteri_, Hyatt.

_Zoarium._ The zoarium consists of a circular or oval mass of no great size. Polyparia do not form compound colonies.

_Polypides._ The polypides lie semi-recumbent in the mass and never stand upright in a vertical position.

_Statoblasts._ The statoblasts are of considerable size and normally bear at both ends a series of chitinous processes armed with double rows of small curved spinules.

As a rule the genus is easily recognized by means of the statoblasts, but sometimes the processes at the ends of these structures are absent or abortive and it is then difficult to distinguish them from those of _Lophopus_. There is, however, no species of that genus known that has statoblasts shaped like those of the Indian species of _Lophopodella_.

Three species of _Lophopodella_, all of which occur in Africa, have been described; _L. capensis_ from S. Africa, which has the ends of the statoblast greatly produced, _L. thomasi_ from Rhodesia, in which they are distinctly concave, and _L. carteri_ from E. Africa, India and Japan, in which they are convex or truncate.

The germination of the gemmule and the early stages in the development of the polyparium of _L. capensis_ have been described by Miss Sollas (Ann. Nat. Hist. (8) ii, p. 264, 1908).

37. Lophopodella carteri (_Hyatt_). (Plate III, figs. 4, 4_a_.)

_Lophopus_ sp., Carter, Ann. Nat. Hist. (3) iii, p. 335, pl.
viii, figs. 8-15 (1859).

? _Lophopus_ sp., Mitchell, Q. J. Micr. Sci. London (3) ii,
p. 61 (1862).

_Pectinatella carteri_, Hyatt, Comm. Essex Inst. iv, p. 203
(footnote) (1866).

_Pectinatella carteri_, Meissner, Die Moosthiere
Ost-Afrikas, p. 4 (in Mobius's Deutsch-Ost-Afrika, iv,
1898).

_Lophopodella carteri_, Rousselet, Journ. Quek. Micr. Club,
(2) ix, p. 47, pl. iii, figs. 6, 7 (1904).

_Lophopus carteri_, Annandale, Rec. Ind. Mus. ii, p. 171,
fig. 3 (1908).

_Lophopodella carteri_, _id._, _ibid._ v, p. 55 (1910).

_Zoarium._ The zoarium as a rule has one horizontal axis longer than the other so that it assumes an oval form when the polypides are expanded; when they are retracted its outline is distinctly lobular. Viewed from the side it is mound-shaped. The polypides radiate, as a rule in several circles, from a common centre. The ectocyst is much swollen, hyaline and colourless.

_Polypide._ The polypide has normally about 60 tentacles, the velum at the base of which is narrow and by no means strongly festooned. The stomach is yellow or greenish in colour. The extended part of the polypide measures when fully expanded rather less than 3 mm., and each limb of the lophophore about the same.

_Statoblast._ The statoblast is variable in shape and size but measures on an average about 0.85 × 0.56 mm. The ends are truncate or subtruncate; the capsule is small as compared with the swim-ring and as a rule circular or nearly so. The processes at the two ends are variable in number; so also are their spinules, which are arranged in two parallel rows, one row on each side of the process, and are neither very numerous nor set close together; as a rule they curve round through the greater part of a circle and are absent from the basal part of the process.

A=outline of a zoarium with the polypides expanded, as seen from below through glass to which it was attached, × 4; B=outline of a zoarium with the polypides highly contracted, as seen from above, × 4; C=statoblast, × 75.]

37 _a._ Var. himalayana.

_Lophopus lendenfeldi_, Annandale (_nec_ Ridley), J. As.
Soc. Bengal, (n. s.) iii, 1907, p. 92, pl. ii, figs. 1-4
(1907).

_Lophopus lendenfeldi_ var. _himalayanus_, _id._, Rec. Ind.
Mus. i, p. 147, figs. 1, 2 (1907).

_Lophopus himalayanus_, _id._, _ibid._ ii, p. 172, fig. 4
(1908).

This variety differs from the typical form in having fewer tentacles and in the fact that the marginal processes of the statoblast are abortive or absent.

_Pectinatella davenporti_, Oka[BL] from Japan is evidently a local race of _L. carteri_, from the typical form of which it differs in having the marginal processes of the statoblast more numerous and better developed. The abortive structure of these processes in var. _himalayana_ points to an arrest of development, for they are the last part of the statoblast to be formed.

[Footnote BL: Zool. Anz. xxxi, p. 716 (1907), and Annot.
Zool. Japon. vi, p. 117 (1907).]

TYPES. The statoblasts mounted in Canada balsam by Carter and now in the British Museum must be regarded as the types of the species named but not seen by Hyatt. The types of the var. _himalayana_ are in the Indian Museum and those of the subspecies _davenporti_ presumably in the possession of Dr. Oka in Tokyo.

GEOGRAPHICAL DISTRIBUTION.--The typical form occurs in Bombay, the W. Himalayas and possibly Madras, and its statoblasts have been found in E. Africa; the var. _himalayana_ has only been taken in the W. Himalayas and the subspecies _davenporti_ in Japan. Indian localities are:--BOMBAY PRESIDENCY, Igatpuri Lake, W. Ghats (alt. _ca._ 2,000 feet); the Island of Bombay (_Carter_): W. HIMALAYAS, Bhim Tal, Kumaon (alt. 4,500 feet).

BIOLOGY.--_L. carteri_ is found on the lower surface of stones and on the stems and leaves of water-plants, usually in lakes or large ponds. Although the zoaria do not form compound colonies by secreting a common membrane or investment, they are markedly gregarious. The most closely congregated and the largest zoaria I have seen were assembled amongst a gelatinous green alga of the genus _Tolypothrix_[BM] (Myxophyceæ) that grows on the vertical stems of a plant at the edge of Igatpuri Lake; it is noteworthy that in this case the alga seemed to take the place of the common investment of _Pectinatella burmanica_, in which green cells are present in large numbers (p. 237). The zoaria of _L. carteri_ are able to change their position, and I found that if a number of them were placed in a bottle of water they slowly came together at one spot, thus apparently forming temporary compound colonies. Before a movement of the whole zoarium commences its base becomes detached from its support at the anterior end (fig. 32, p. 172), but the whole action is extremely slow and I have not been able to discover any facts that cast light on its exact method of production. At Igatpuri statoblasts are being produced in considerable numbers at the end of November, but many young zoaria can be found in which none have as yet been formed.

[Footnote BM: Prof. W. West will shortly describe this alga,
which represents a new species, in the Journ. Asiat. Soc.
Bengal, under the name _Tolypothrix
lophopodellophila_.--_April 1911_.]

The larva of a fly of the genus _Chironomus_ is often found inhabiting a tube below zoaria of _L. carteri_. It is thus protected from its enemies but can protrude its head from beneath the zoarium and seize the small animals on which it preys.

Genus 4. PECTINATELLA, _Leidy_.

_Cristatella_, Leidy, P. Ac. Philad. v, p. 265 (1852).

_Pectinatella_, _id._, _ibid._, p. 320.

_Pectinatella_, Allman, Mon. Fresh-Water Polyzoa, p. 81
(1857).

_Pectinatella_, Hyatt, Proc. Essex Inst. v, p. 227, fig. 20
(1867).

_Pectinatella_, Kraepelin, Deutsch. Süsswasserbryozoen, i,
p. 133 (1887).

_Pectinatella_, Oka, Journ. Coll. Sci. Tokyo, iv, p. 89
(1891).

TYPE, _Pectinatella magnifica_, Leidy.

This genus is closely allied to _Lophopodella_, from which it is often difficult to distinguish young specimens. Adult zoaria are, however, always embedded together in groups in a gelatinous investment which they are thought to secrete in common[BN], and the statoblasts are entirely surrounded by processes that bear curved spinules at their tips only. The polypides have the same semi-recumbent position as those of _Lophopodella_ but are larger than those of any species of _Lophopodella_ or _Lophopus_ yet known. The statoblasts are larger than those of any other Plumatellidæ.

[Footnote BN: It is now perhaps open to doubt whether the
investment is actually secreted by the polyzoon, for Prof.
W. West has discovered in it the cells of an alga belonging
to a genus which habitually secretes a gelatinous investment
of its own (see p. 238, _post._).--_April 1911._]

The type-species was originally found in N. America but has since been taken in several localities in continental Europe. Except this and the Indian form only one species is known, namely _P. gelatinosa_ from Japan. _P. magnifica_ has circular statoblasts with long marginal processes, while in _P. gelatinosa_ the statoblasts are subquadrate and in _P. burmanica_ almost circular, both Asiatic forms having very short marginal processes.

The compound colonies formed by _Pectinatella_ are often of great size. Those of _P. gelatinosa_ are sometimes over 2 metres in length, while those of _P. burmanica_ in the Sur Lake appeared to be only limited as regards their growth by the shallowness of the water in which the reeds to which they were attached were growing. Some were observed that were over 2 feet long.

38. Pectinatella burmanica, _Annandale_. (Plate III, fig. 5.)

_Pectinatella burmanica_, Annandale, Rec. Ind. Mus. ii,
p. 174, fig. 5 (1908).

_Pectinatella burmanica_, _id._, _ibid._ v, p. 56 (1910).

_Pectinatella burmanica_, _id._, Spol. Zeyl. vii, p. 63,
pl. i, fig. 3 (1910).

_Zoarium._ The zoaria are circular or nearly so except when about to undergo division, in which case they are constricted in the middle. As a rule they measure nearly an inch (2 cm.) in diameter. The polypides have a definite arrangement in each zoarium, being divided into four groups, each of which has a fan-like form. In the first place they are separated into two main divisions in a line running through the centre of the zoarium, and secondly each main division is separated into two subordinate ones in a line running across the other at right angles. The number of zoaria joined together in a single compound colony is very variable; sometimes there are only about half a dozen and sometimes several hundreds. The common investment in living colonies is often as much as two inches thick and has a translucent dark greenish colour due to the presence in it of green cells.

A=polypide with the lophophore expanded, × 15; _a_=oesophagus; _b_=cardiac limb of stomach; _c_=stomach; _d_=rectum; _e_=anus; _f_=funiculus. [The muscles are omitted and the external tubercles are only shown on part of the polypide. The specimen is from the Sur Lake, Orissa.] B=statoblast from Ceylon, × 35.]

_Polypide._ The polypide can be extruded for a distance of at least 5 mm. Its whole external surface is covered with minute tubercles. There are about 90 tentacles, which are long and slender, the velum at their base being narrow and almost straight. The stomach is of considerable stoutness.

_Statoblast._ The statoblasts are of large size, measuring from 1 to 1.75 mm. in diameter. In form they are almost circular, but one side is always slightly flattened. The marginal processes are very short and bear a single pair of hooks at the tip. The capsule is circular and small as compared with the free part of the swim-ring.

TYPE in the Indian Museum.

_P. burmanica_ is evidently a near relation of _P. gelatinosa_, Oka, from Japan, differing from that species in the shape of the statoblasts and in having much longer tentacles. The arrangement of the polypides in the zoarium and the general structure of the statoblasts are very similar in the two species.

GEOGRAPHICAL DISTRIBUTION.--_P. burmanica_ was originally described from a swamp at Kawkareik in the Amherst district of Tenasserim but has also been found in the Sur Lake near Puri in Orissa. Dr. A. Willey obtained specimens from a pool by the roadside between Maradankadewela and Galapitagala, at the foot of Ritigala, N. Central Province, Ceylon.

BIOLOGY.--The first specimen obtained was a statoblast fixed to a tube of the oligochæte worm _Aulophorus tonkinensis_ taken at Kawkareik in March. At the same time young zoaria, which did not yet possess a common investment, were found on a leaf growing on a twig which drooped into the water. Large compound colonies were taken in Orissa in October. They completely encased the stems of reeds, thus forming hollow cylinders, but slipped from their supports when the reeds were pulled out of the water. In life they resembled gelatinous algæ rather than animals and exhibited a striking similarity to masses of zoaria of _Lophopodella carteri_ surrounded by such algæ. Some of the colonies were evidently dying and contained few polypides in a living condition, but many statoblasts; others were in a flourishing condition and were producing larvæ and statoblasts simultaneously.

A piece of a colony full of larvæ was placed before midday in an aquarium, which was kept in a shady verandah. Large numbers of larvæ were set free almost immediately. They measured about 2 mm. in length and were distinctly pear-shaped; each contained a pair of polypides, which occupied a comparatively small part of the interior, the whole of the broader half being hollow. The larvæ swam slowly, broad-end-first, by means of the cilia with which their surface was covered, occasionally gyrating on their long axis and always adopting an erratic course. Towards evening they showed signs of settling down, frequently touching the glass of the aquarium with their broad ends and sometimes remaining still in this position for some minutes. Many attempts were, however, made before fixation was completed, and this did not occur until after nightfall. By next morning every larva was fixed to the glass and had everted its two polypides. Unfortunately I was not able to trace the development further, but young compound colonies were found in which the secretion of the common investment had just commenced. The zoaria in these colonies measured about 1 cm. in diameter and already contained many polypides each.

Oka has described the development from the statoblast of the allied Japanese species. He found that each statoblast produced in the first instance a single polypide, and that the statoblasts, which were produced in autumn, lay dormant through the winter and germinated in spring. As the Sur Lake begins to undergo desiccation as soon as the "rains" cease, the statoblasts in it probably do not germinate until the break of the next "rains" about the middle of June. I have had dried statoblasts in my possession for over two years. Their cellular contents appear to be in good condition, although the cells show no signs of development; but they have not germinated in my aquarium, in which some of them have now been kept for more than six months.

The green cells of the common investment are peculiar bodies that deserve further study than it has yet been possible to devote to them. Each cell is of ovoid form, varying somewhat in size but as a rule measuring about 0.03 × 0.008 mm. There can be no doubt that these bodies represent a stage in the life-history of an alga[BO]. Diatoms, bacilli and other minute plants are often present in the membrane as well as the characteristic green cells, but do not form a constant feature of it.

[Footnote BO: Professor W. West identifies this algæ as
_Dactylococcopsis pectinatellophila_, new species. It will
be described, before the publication of this book, in the
Journ. As. Soc. Bengal (1911). Prof. West has found,
associated more or less fortuitously with _P. burmanica_,
another alga, namely _Microcystis orissica_, also a new
species.--_April 1911._]