Chapter XLIV: Part IV: (evertebrata)

Since a large proportion of all those helminths that require a change of hosts must needs pass into the bodies of insects, crustaceans, mollusks, or other evertebrated animals, it is evident that these lower creatures are almost as liable to be infested by parasites as the vertebrates themselves. As a rule, no doubt, the parasitic forms infesting individual evertebrated hosts are not numerous; nevertheless the water-snails form a noteworthy exception. Thus, some ten different species of parasite are found either in or upon the common _Planorbis corneus_; whilst _Lymnæus stagnalis_, _Paludina vivipara_, and _P. impura_, each support at least a dozen species. Of course, the parasites are not sexually mature, since nearly all of them are _Cercariæ_ or larval trematodes. Snails, oysters, mussels, whelks, and other mollusks afford harbour and anchorage to a variety of parasites and messmates; but, fortunately, few or it may be none of the strictly human parasites require to pass through these intermediate bearers. _Distoma crassum_ is possibly an exception. Save the cuttle-fishes, not many evertebrated animals are infested by sexually-mature worms. One of the most notable exceptions is that of a nematoid infesting bees. This worm was known to John Hunter, who spoke of it as “the animal that breeds in the humble bee.” In the year 1836, M. Léon Dufour first applied the term _Sphærularia_ to this remarkable worm, which he discovered in the abdominal cavities of two species of bee (_Bombus terrestris_ and _B. hortorum_). The worm was subsequently found by Von Siebold in two other species of bee (_B. muscorum_ and _B. sylvarum_), but it remained for Sir John Lubbock to demonstrate that this parasite not only infests these insects, but also _Bombus lucorum_, _B. lapidarius_, _B. pratorum_, _B. subterraneus_, and _Apathus vestalis_. I possess specimens from _Vespa vulgaris_ and _V. rufa_. Sir J. Lubbock and Mr. Cole have separately given full anatomical descriptions of the worm. According to Lubbock the so-called female is about an inch in length, of a whitish color, and 1/15″ in thickness, being bluntly pointed at either extremity. _Sphærularia_ is everywhere covered by small warts or button-like projections, in all numbering about 800. The warts are transparent, each, according to Lubbock, projecting from 4/1000″ to 6/1000″ above the general surface of the integument. There is neither mouth, œsophagus, intestine, nor anus; but in their place a large fatty mass or _corpus adiposum_. Sir J. Lubbock remarks that this peculiar organ “is homologous, not with the whole intestinal canal of nematodes, but only with the intestine; and we find, in fact, that in Gordius the œsophagus is very short, and opens at once into the anterior end of the _corpus adiposum_; so that to pass from this genus to _Sphærularia_ it would be necessary to shorten the œsophagus a little more, and then the wall of the _corpus adiposum_ would be immediately attached to that of the body. So far, therefore, as concerns the _corpus adiposum_ and the œsophagus, _Sphærularia_ agrees neither with Gordius nor Mermis, nor, indeed, with one more than the other; since, if it agrees with _Mermis albicans_ in the double series of large fat cells, it has no œsophagus, and in this respect more nearly resembles Gordius.” The reproductive organs consist of a single ovary, uterus, and terminally situated vulva. These organs in the full-grown females contain ova in all stages of development up to the condition of advanced yolk segmentation; but it does not appear that embryonic formation takes place whilst the eggs are still _in utero_. “The young animals are born soon after the eggs are laid. They are about 1/60″ in length, and 1/2500″ in diameter at the broadest part. Before Sir J. Lubbock conducted his inquiries the so-called male appears to have been overlooked. The male, if male it be, is extremely minute; that is to say, about 28,000 times smaller than the female.” Notwithstanding this very circumstantial account based on Lubbock’s determinations, Schneider has sought to show that the facts have been entirely misinterpreted. What Lubbock regards as the male worm is, in Schneider’s opinion, a female, whilst the so-called female is nothing more than a gigantic prolapsed uterus which has become many thousand times larger than the body of the worm whence it proceeded. It must be allowed that Schneider’s description and accompanying figures are very convincing. When revising the entozoa of the Hunterian Collection in 1866 I explained the specimens and dissections in accordance with Lubbock’s views. In the following year Prof. Huxley in his College Lectures supported the view of Schneider, but in his recently published manual the opinions of the Berlin helminthologist are not so much as alluded to.

Another point of special interest in connection with the parasites of insects concerns the development of _Mermis albicans_. At or near the time of the maturation of the ova, the parent worm, hitherto lodged within the body of some insect, buries itself in the soil. It commences its migration by boring its way out of the body of the host. Some difference of opinion exists as to the condition of the parent at the time of its wandering, for Von Siebold asserted that it quitted its parasitical mode of life “in order to become sexually mature away from the animal” infested; whereas Van Beneden states that the embryos are always formed at the time of the wandering.

From Von Siebold’s experiments it would appear that incompletely developed Mermes can become mature whilst still in the soil; but the normal condition requires the wandering to commence, as we have said, at or near the full time of embryonal development. The embryos are reproduced viviparously, and being set free, they pass a certain period of their existence in the soil. Here they grow rapidly, acquire sexual organs, and subsequently seek to “gratify their immigrative propensities,” as Von Siebold says, by selecting and penetrating the soft-bodied larvæ of lepidopterous and other insects. This entrance they accomplish by means of a sharply-pointed dentule or boring stylet, which at the time of disuse is concealed within the head. Having once gained access to the host they remain within its body until the caterpillar has become transformed into the perfect butterfly, or until their own sexual maturity is completed. Van Beneden thinks it probable that the males quit the host some time before the females, a view which, if correct, might alone account for the comparative scarcity of the males. According to Von Siebold, sexual congress occurs before the entrance of the worm into the caterpillar. This observation agrees with the generally admitted fact that hitherto no male Mermes have actually been detected in the bodies of insects. The Gordii, like Mermes, become free in damp earth and penetrate the bodies of certain insects or their larvæ. Some of them gain access to fishes. Like the free nematodes (_Anguillulidæ_), many of the Gordii will survive complete desiccation. The eggs of the mature worms are deposited in long agglutinated chains in water or damp situations.

I must conclude. In the body of this work will be found many notices of insect parasites that are awaiting transference to some vertebrate. I need only allude to the rôle of the mosquito, to that of the louse of the dog, and especially to that of the little myriapod (_Glomeris_) which, like the common glow-worm (_Lampyris_), possesses phosphorescent properties. I mention this again partly in correction of an entomological error (at p. 296) which escaped me at the time of going to press. Leidy has described a mature nematode (_Ascaris infecta_) from _Passalus cornutus_, and numerous Filariæ are known to infest insects (_Blatta_, _Forficula_, _Phosphuga_, &c., &c.). From an earwig I obtained a filaria nearly five inches in length.

We have seen that the larvæ of _Dracunculus_, _Cucullanus_, as well as those of other important nematodes, dwell in bodies of entomostracous crustacea, whilst those of _Echinorhynchus_ attack the Gammari and their allies. The well-known _Udonella caligorum_ attaches itself to crustacea that are themselves parasitic.

As many of the so-called free nematodes live in the slime of animals, Villot is of opinion that no very distinct line of demarcation can fairly be drawn between the parasitic and free species. This work, however, having dealt only with genuine parasites, I have purposely omitted any detailed account of the so-called free nematoids. I mention this lest it should be supposed that I had shown a studied neglect of the more or less remarkable labours of Bütschli, Bastian, Eberth, Linstow, Marion, Villot, Claus, De Man, Carter, and many others.

BIBLIOGRAPHY (No. 60).--_Bastian, H. C._, “Monograph on the Anguillulidæ, or free Nematoids, marine, land, and freshwater, with description of 100 new species,” ‘Linnean Trans.’ for 1865, vol. xxv, p. 73.--_Idem_ (see Bibliog. No. 2).--_Idem_, “Free Nematoids,” being an article in the ‘Popular Science Review’ for 1868, vol. vii, p. 163.--_Brady, G. S._, ‘Monograph of the free and semiparasitic Copepoda,’ London, 1878.--_Bütschli, O._, “Untersuchungen ueber freilebende Nematoden und die Gattung Chætonotus,” ‘Sieb. und Köll. Zeitschrift,’ 1876.--_Carter, H. J._, “On a Bisexual Nematoid Worm which infests the common House-fly (_Musca domestica_),” ‘Ann. Nat. Hist.,’ 1861, and in the ‘Bombay Med. and Phys. Soc. Trans.,’ new series, 1860.--_Claparède_ (see Panceri).--_Claus, C._, ‘Beobachtungen ueber d. Organis. und Fortpflanz. v. _Leptodera appendiculata_,’ 1869.--_Cobbold_, “Note on Insect Parasites,” in ‘Rep. of Entomological Club,’ in the ‘Midland Naturalist,’ March, 1878, p. 80.--_Cole, W._, “Remarks on a Parasite of Humble Bees,” in ‘Journal of the Quekett Microscopical Club,’ 1875.--_Dufour, L._, “Sphærularia,” ‘Ann. des Sci. Nat.,’ 1836.--_Dujardin_, “On Mermis,” ‘Ann. des Sci. Nat.,’ 2e sér., tom. 18, p. 129.--_Eberth_ (see Bibliog. No. 2).--_Garner, R._, “Note on a Distoma,” in his paper ‘On the Lamellibranchiate Conchifera,’ ‘Trans. Zool. Soc.,’ 1841.--_Ghaleb, O._, “Observations and Experiments on the Migrations of _Filaria rhytipleurites_, a Parasite of Cockroaches and Rats,” ‘Comptes Rendus,’ July 8, 1878, and ‘Ann. Nat. Hist.,’ Aug., 1878.--_Idem_, “Note sur l’anat. et les migrations de deux Nématoides parasites, le _Pæcilogaster blatticola et Fil. rhytipl._,” Paris, 1876 (quoted by O. von Linstow).--_Giard, M. A._, “On the parasitic Isopoda of the genus Entoniscus (infesting Crustacea),” from ‘Comptes Rendus,’ Aug., 1878, in ‘Ann. Nat. Hist.,’ Otc., 1878.--_Idem_, “On the Orthonectida, parasitic on Echinodermata and Turbellaria (Rhopalura),” ‘Ann. Nat. Hist.,’ Feb., 1878.--_Grube, A._, “On Cyclops as a new Cestoid-bearing Host,” from ‘Zoologisch. Anzeiger,’ Bd. i, s. 74, in ‘Journ. Royal Microsc. Soc.,’ Nov., 1878, p. 254.--_Hunter, J._, “Filaria of the Bee,” in ‘Catal. (by Owen) of the contents of the Mus. Royal Coll. Surg.,’ part iv, fasc. i, p. 37, 1830.--_Kynston_, “Worms attached to a Grasshopper,” ‘Proc. Ashm. Soc.,’ in ‘Corbyn’s India Review,’ and in ‘Journ. of Foreign Sci.,’ 1837, p. 172.--_Lima, J. F. da S._, “Remarks on the _Filaria medinensis_ or Guinea-worm; on the occurrence of this parasite in the Province of Bahia; and on its entrance into the human body by drinking water;” trans. from the Portuguese by Dr J. L. Paterson, and pub. in the ‘Veterinarian’ for Feb., 1879 _et seq._--_Linstow_, “Helminthologische Beobachtungen,” in ‘Archiv für Naturgeschichte,’ 1876.--_Lubbock, Sir J._, “On _Sphærularia bombi_,” ‘Nat. Hist. Rev.,’ 1861.--_Idem_, “Notes,” &c., _ibid._, 1864, p. 265.--_Mason, J. W._, “Note on the Geographical Distribution of the _Temnocephala chilensis_ (parasitic upon a freshwater crayfish, _Paranephrops setosus_, in New Zealand),” ‘Annals Nat. Hist.,’ 1875, p. 336.--_Marion, A. F._, ‘Revision des Nématodes (&c.),’ Marseilles.--_Maund, B._, “A description of _Filaria forficulæ_,” ‘Rep. Proc. Linn. Soc.,’ in ‘Zool. Journ.,’ 1832-34, p. 263.--_Meissner_ (see Thomson).--_Owen, R._ (see Hunter).--_Pagenstecher_ (see Bibl. No. 58).--_Panceri, P._ (e di E. D. Claparède), “Nota sopra une alciopide parassito dell _Cydippe densa_,” ‘Mem. della Soc. Ital. di Sci. Nat.,’ 1867.--_Sars_, “Intestinal Worm in an Acaleph.,” from ‘Wiegmann’s Archiv,’ in ‘Ann. Nat. Hist.,’ 1845.--_Siebold, C. J. von_, in ‘Wiegmann’s Arch.,’ 1835.--_Idem_, in ‘Ray Soc. Rep.’ (by Busk), 1847.--_Idem_, “Worms,” &c., _ibid._, p. 503, 1847.--_Idem_, “Report on Helminthology, and on the Nemertinæ” (trans. by W. B. Macdonald, in ‘Ray Soc. Rep. on Zool.,’ 1842, p. 280), Edinburgh, 1845.--_Idem_ (see Thomson).--_Thomson, A._ (for review of the writings of Meissner, Von Siebold, and others, respecting the development of Mermis, Gordius, &c., see the classical and elaborate art. “Ovum”), in ‘Supp. to Todd’s Cyclop.,’ 1859.--_Vogt, C._, “On some Inhabitants (Cercariæ) of the Fresh-water Mussels,” from ‘Ann. des Sci. Nat.,’ in ‘Ann. Nat. Hist.,’ 1850.--_Whitman, C. O._, “The Embryology of Clepsine (with valuable Bibliography),” ‘Quart. Journ. Micr. Sci.,’ July, 1878.