PART V (Pinnipedia).

Following the order of classification adopted in my description of the Mammalia in the ‘Museum of Natural History,’ I proceed to speak of the internal parasites of the seals (Phocidæ) and walruses (Trichecidæ). From their piscivorous habits one would naturally expect the seals to be largely infested with entozoa, and yet, though sufficiently victimised, they are not liable to entertain so great a variety of helminths as the fishes themselves on which they feed.

Fig. 59.—Ascaris os­cu­la­ta. a, Male; b, fe­male. Nat­ural size. Orig­inal.

The flukes observed in Phoca vitulina are Distoma acanthoides and Amphistoma truncatum, the latter occurring also in P. grœnlandica. In another seal (P. barbata) we have D. tenuicolle. The nematodes are more numerous. The best-known is the maw-worm (Ascaris osculata), which seems to be always present in full-grown seals of every kind. In the years 1862–64 I conducted a series of experiments with the eggs of this worm. I reared embryos both in salt and fresh water, but the administration of the young worms to various animals led to no result. However, I succeeded in watching the growth of the embryos until they had acquired well-marked digestive organs and a length of 1/25″, their size when emerging from the egg-shell in the water having been about 1/150″ only. The large strongyle (Eustrongylus gigas) has been found in various organs of the common seal. Of more interest are the Filariæ found in the heart of seals, which in many respects resemble those obtained from the same situation in dogs. Professors Joly, Leidy, and myself, have each described a species, but apparently our descriptions all refer to one and the same parasite. It has also been seen by Camill Heller. The close correspondency in size and other characters of Leidy’s Filaria spirocauda and my Filaria hebetata leaves little doubt as to their identity. As the worms were both originally noticed by Leidy and Joly in 1858, I cannot pronounce upon the question of priority of discovery. By Joly the worm was called F. cordis phocæ. In Leidy’s and in my own specimens the males were four inches long, and the females six inches; they extended up to 8″ in some of the American examples. The worms found by Prof. Joly were all females. Professor Millen Coughtrey, who furnished me with the seal’s heart, stated that it was obtained from a male hoodcap (Stemmatopus cristatus), a rare visitant of our British coasts. This seal was captured on the Cheshire side of the Mersey river. Leidy and Joly obtained their specimens from Phoca vitulina. In the common seal have also been found Ligula crispa, Schistocephalus dimorphus, and Echinorhynchus strumosus. In other seals a not uncommon tapeworm of the Bothriocephalous type is that called Dibothrium hians by Diesing. To Prof. Krabbe I am indebted for a specimen of Bothriocephalus fasciatus taken from Phoca hispida. There is a nematode of frequent occurrence in P. hispida and P. grœnlandica. This is the Ophiostoma dispar of Rudolphi. In addition to the above I can only add that P. barbata is infested by Liorhynchus gracilescens, occupying the stomach, and by a tapeworm, Tetrabothrium anthocephalum, which is found in the lower part of the large intestine.

Bibliography (No. 46).—Cobbold, “Description of F. hebetata,” in ‘Notes on Entozoa,’ part i, sp. 3, ‘Proc. Zool. Soc.,’ Nov. 18th, 1873, p. 741.—Idem, “On Ascaris osculata,” in ‘Report of Experiments respecting the development and migrations of the Entozoa;’ ‘Brit. Assoc. Trans.,’ 1864, p. 114.—Heller, C., in ‘Schrift der zool.-botan. Gesellsch.,’ Wien, 1858, s. 83.—Joly, “On a new Species of Hæmatozoon of the genus Filaria, observed in the heart of a seal;” from ‘Compt. Rend. Acad. Sci.,’ 1856, p. 403, in ‘Ann. Nat. Hist.,’ vol. i, 3rd ser., 1858; also abstr. in the ‘Year Book,’ 1859.—Leidy, J., (E. spirocauda) in ‘Proc. Philad. Acad.,’ 1858, p. 112.