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.
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.
[Illustration: FIG. 59.--_Ascaris osculata._ _a_, Male; _b_, female.
Natural size. Original.]
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.