Though very numerous, the parasites of this order are chiefly
interesting as embracing those of the hares and rabbits, moles, mice,
rats, squirrels, and beavers. Some slight notice, however, will be given
of the entozoa of each of the eleven families into which the order may
be divided.
The squirrels (_Sciuridæ_) are liable to be infested by the common liver
fluke (_F. hepatica_), and also, it is said, by a cysticercus (_C.
tenuicollis_). I have never encountered this bladder worm, but in 1864 I
described some polycephalous hydatids (_Cœnuri_) which I obtained from
the viscera of an American squirrel. I think the host was of the same
species (_Sciurus vulpinus_) as that from which Mr Chapman has since
obtained an example of Echinorhynchus (_E. moniliformis_). This worm
also infests the hamster. A very small female round worm, probably a
strongyle, was described by Rudolphi as _Ascaris acutissima_. It infests
the cæcum of the common squirrel, in which host a species of tapeworm
is tolerably frequent (_Tænia dendritica_). The common European marmot
is infested by _T. pectinata_, so abundant in hares and rabbits. I
have also noticed it as occurring in the Canadian porcupine (_Hystrix
dorsata_). The dormice (_Myoxidæ_) are not much troubled with parasites,
at least I have not encountered any in our common _Myoxus avellanarius_.
In _M. glis_, however, a tapeworm, and at least one species of strongyle
(_S. gracilis_), have been observed. Dujardin described very fully
another strongyle (_S. lævis_) from _M. nitela_, from the long-tailed
field-mouse (_Mus sylvatica_), and from _Arvicola subterraneus_. The
other species are _Trichosoma myoxi nitelæ_, and _Ophiostoma cristatum_
from _Myoxus dryas_, and _M. muscardinus_. The jerboas (_Dipodidæ_),
in common with the hamster and several species of true mice, are apt to
be infested by _Ascaris tetraptera_; and a small nematoid, apparently
immature, was noticed by Otto in the intestines and in the abdominal
walls and cavity of _Dipus tetradactylus_. Mice, properly so called, are
largely infested, as is also the hamster (_Cricetus vulgaris_), which I
include in the _Muridæ_. In addition to the parasites already mentioned,
the hamster is infested by _Tænia straminea_. Along with examples of
this tapeworm I have received from Dr Murie some acephalocysts found in
a hamster which died at the Zoological Gardens.
Flukes exist in the long-tailed field-mouse (_Distoma vitta_ and _D.
recurvum_), but I have not seen any in our common mice and rats.
However, Dujardin describes a distome (_D. spiculator_) in the brown
rat (_Mus decumanus_). One of the tapeworms observed in the mouse (_M.
musculus_) is _Tænia pusilla_, also found in the rat (_M. rattus_)
and long-tailed field-mouse. The house-mouse likewise harbors _T.
microstoma_ and _T. leptocephala_; and an immature cestode has also been
seen in the abdomen, probably a species of _Ligula_. Various species of
rat also harbor _T. diminuta_. In regard to the round worms one of the
most common species is _Ascaris oxyura_. This not only occurs in rats
and mice, but also in voles, water-rats, and many other rodents. The
rodents’ whipworm (_Trichocephalus nodosus_) is yet more common in the
lemmings, rats, voles, and mice; another species (_T. unguiculatus_),
taking its place in hares and rabbits, and yet another (_T. affinis_)
in the porcupine. Another nematoid, very common in mice, is _Spiroptera
obtusa_, occupying the stomach. I have seen a mouse with its abdomen so
distended by their presence that the animal could scarcely run along the
pathway where it was killed by being trod upon. According to Marchi,
the young of this entozoon dwell in the fat surrounding the alimentary
canal of the larva of an insect (_Tenebrio molitor_). When noticing the
parasites of the cat I referred to Leuckart’s interesting discovery
of the relations subsisting between the adult _Olulanus tricuspis_,
found in the stomach walls of that feline, and the immature encysted
worms, found not only as wanderers in the cat itself but also in the
muscles of mice. The olulanised mouse is thus an intermediate host.
Rats and mice also play the part of intermediary bearers in the case of
two other species of entozoa, namely, _Trichina spiralis_ and _Tænia
crassicollis_, the tænioid scolex or larval condition of the cat’s
tapeworm being familiarly known as _Cysticercus fasciolaris_. This
sexually-immature tapeworm infests many other rodents, especially the
voles (_Arvicolidæ_). In regard to _Trichinæ_ it must not be forgotten
that their presence in rats is not uncommon in some parts of Europe;
and this circumstance may explain the recurrence of trichinosis (first
in hogs and then in man) in certain outlying districts. Only in this
way can the Cumberland outbreak in this country be accounted for. Here
I cannot dwell upon the subject, but in this connection I may observe
that Bakody has in a very convincing manner described a new variety or
species of Trichina, found by him infesting the walls of the stomach
and intestine of rats. In the first instance he detected the worm in
association with the ordinary _T. spiralis_, but afterwards separately.
He also obtained it in fowls. The species should be called _Trichina
Bakodyii_. Possibly the nematodes observed by Colin in 1863 also refer
to this worm. They occupied tubercles in the liver of a rat. In regard
to the beavers (_Castoridæ_) it appears that they harbor many species
of round worms, and also several flukes, but they do not appear to have
been very much studied. In Morgan’s work on the American beaver there is
a notice in which it is stated that Dr Ely found a very fine filamentous
worm 40‴ in length. This does not seem to correspond with _Ascaris
castoris_ (Rud.). He also speaks of large numbers of a slender white
worm, 3″ to 5″ in length, found in the peritoneal cavity, and referable
to the genus _Filaria_. This cannot be confounded with _Trichocephalus
castori_ (Rud.). Moreover, he describes a strongyle (_Sclerostoma_)
as infesting the colon, and especially the cæcum. These all appear
to be new to science. The _Fasciola hepatica_ is occasionally found
in the liver, but the most common helminth of beavers is _Amphistoma
subtriquetrum_. Specimens of this worm may be seen in the British and
Hunterian Museums. As regards the porcupines (_Hystricidæ_) I have
already mentioned the occurrence of a tapeworm in the common species.
The larval _Pentastoma denticulatum_ has been found by Otto attached to
the surface of the lungs, and Redi, about two centuries back, noticed
small nematodes lodged in tubercles of the œsophagus. The late C. M.
Diesing obtained _Trichocephalus affinis_ from the intestines. So far as
I am aware, little or nothing has been said respecting the helminths of
the _Octodontidæ_, _Chinchillidæ_, and _Cavidæ_. Like other European
investigators I have dissected guinea pigs (_Cavia aperœa_) without
finding any parasites; but in Brazil a small species of ascaris (_A.
uncinata_) was found by Natterer in this animal and also in the paca
(_Cœlogenys paca_). The agoutis (_Dasyprocta_) harbor _Trichocephalus
gracilis_.
The entozoa of the duplicidentate rodents (_Leporidæ_) acquire
importance from the fact of their abundance and from the intimate
relation which some of them bear to parasites infesting the dog and
other animals. Thus, the two commonest kinds of fluke infesting
cattle (_Fasc. hepatica_ and _Dist. lanceolatum_) also attack hares
and rabbits; the former parasite often producing the rot disease,
which is almost as fatal to the rodents as it is to the ruminants.
Mutual infection occasionally results from this circumstance by the
distribution of germs. All experiment-conducting helminthologists have
reared _Tænia serrata_ from the _Cysticercus pisiformis_; nevertheless,
several English Manuals of Zoology persist in propagating the old
error of Von Siebold, who supposed he had reared this tapeworm by the
administration of Cœnuri. So far as I am aware, no feeding experiments
have been conducted with the Cœnuri of rabbits (_C. cuniculi_). These
bladderworms infest the soft parts of the body, often producing tumours
having a very unsightly appearance. For details I must refer to the
papers quoted below. The Norfolk warreners call the infested hosts
“bladdery rabbits.” Though apparently most abundant in the eastern
counties of England, these diseased rabbits are by no means confined
to that quarter. Through Mr Alston’s help I have received specimens
of _Cœnurus cuniculi_ from Ayrshire, Scotland. Probably this form of
Cœnurus occurs wherever rabbits live. In Italy a case is recorded
by Perroncito from the abdominal cavity of a rabbit (_coniglio_).
Every experimenter is more or less familiar with the cestode larvæ
(_C. pisiformis_) found wandering in the abdominal cavity. These
were regarded as flukes by Kuhn (_Monostoma leporis_). I need hardly
remark that the developmental and structural changes undergone by
these Cysticerci during their residence within the rabbit have been
exhaustively followed out and treated of by Leuckart. Without dwelling
on this subject, I must in justice add that in this relation the
special labors of Küchenmeister, Van Beneden, Haubner, Wagener, Röll,
Eschricht, and Möller played no inconspicuous part. My own efforts
in 1857, and subsequently, were not unattended with success. It
therefore seems to me, without prejudice to the recent experiences of
De Sylvestre and others, that further experiments in this immediate
connection are unnecessary. As regards the nematodes of leporine
rodents, probably the most important is _Strongylus commutatus_. This
parasite, like its husk-producing congeners, infesting calves and
lambs, occasionally sweeps off great numbers of hares. Such an epizoöty
occurred in Thuringia in 1864. The most frequent intestinal parasite
of rodents is probably _Oxyuris ambigua_, but _Strong. retortæformis_
is tolerably abundant in the hare, and _Trichocephalus unguiculatus_
is liable to occur in all leporines. I know nothing of the so-called
_Strong. strigosus_ of rabbits, but Bellingham found it in Ireland.
Olfers and Natterer obtained a small ascaris (_A. veligera_) from
_Lepus braziliensis_; but I cannot help thinking that the large measle
(_Cysticercus macrocystis_) described by Diesing as three inches in
length, and obtained from the same rodent, must either have been
_Cœnurus cuniculi_ or else another form of polycephalous hydatid.
In reference to the ectozoa of rodents it may be said that they are very
numerous. Acari infest rats and mice, and especially leporines. Thus,
in the mouse are found _Sarcoptes notoedre_, Bourguignon, var. _muris_,
Mégnin, _Sarc. musculinus_, Koch, and _Myobia musculi_, Claparède. It
is not very generally known that wild rabbits are apt to be attacked
by the common autumnal spider (_Leptus autumnalis_), whence, as once
happened with myself, they may be transferred to the human body. The
ears of tame rabbits are sometimes covered with acari, which are easily
destroyed by the cautious application of a mixture of carbolic acid and
olive oil (one of acid to six of the oil). Rodents also harbor fleas.
At a meeting of the Entomological Society in 1875 Mr Vernall showed
living specimens from the ears of a rabbit, and Messrs Cole and W. A.
Lewis stated that they had obtained fleas from the hedgehog and European
marmot respectively.
BIBLIOGRAPHY (No. 47).--_Beneden_ (see Van Beneden below).--_Capelle,
J._, Extr. from a letter, in which the author states that he had
“found worms of the tænia kind in the liver of sixteen out of eighteen
rats,” ‘Med. Commentaries,’ vol. xix, p. 139, 1794; see also ‘Trans.
Coll. Phys. of Philad.,’ vol. i, part ii, p. 60, 1793.--_Chapman, H.
C._, “Echinorhynchus in Squirrel,” ‘Proc. Acad. Philad.,’ 1874, p.
76.--_Cobbold_, “Note on Cœnurus (from a squirrel),” ‘Proc. Linn.
Soc.,’ May 5, 1864.--_Idem_, “On the occurrence of _Tænia pectinata_
in the Porcupine (_Hystrix dorsata_),” in a letter to Dr. Lawson in the
‘Canadian Naturalist and Geologist,’ 1862.--_Idem_, ‘On _T. serrata_,’
&c. (see Bibl. No. 45).--_Colin_, “On the presence of a Nematode Worm in
certain Tubercles of the Liver of a Rat,” from ‘Rec. de Méd. Vét.,’ in
‘Edin. Vet. Rev.,’ Oct., 1863.--_Leuckart_, ‘Die Blasenbandwürmer (u. s.
w.),’ 1858 (contains numerous details and figs. in ref. to _Cysticercus
pisiformis_ and _T. serrata_, &c.).--_Marchi, P._, ‘Mem. della R. Accad.
d. Sci. di Torino,’ xxv.--_Peacock_, “Remarks on the Liver of a Mouse
with Cysts containing Cysticerci,” ‘Lancet’ and ‘Trans. Path. Soc.,’
1855.--_Perroncito, E._, “Sopra un caso di Cœnurus (in the abdominal
cavity of a rabbit),” ‘Giornale Med. Veter.,’ 1876.--_Siebold_ (see Von
Siebold, below).--_Sylvestri, De_, “Experiments with _C. pisiformis_,”
‘Il. Med. Veterinario,’ 1871.--_Van Beneden_ (see Bibl. No.
45).--_Idem_, “On _Sciurus glacialis_ and its Parasites,” from ‘Bull. de
l’Acad. de Belgique,’ in ‘Ann. Nat. Hist.,’ vol. xiii, 1854.--_Verrall_,
in ‘Proc. Ent. Soc. Lond.,’ Feb. 15, 1875, p. 3.--_Von Siebold_, ‘Ueber
die Band-und Blasenwürmer,’ Leipsig, 1854, and Huxley’s edit. for Syd.
Soc., 1857.--_Idem_, “Experiments on the Transformation of the Cystoid
Worms into Tænias,” from ‘Ann. des Sci. Nat.,’ in ‘Ann. Nat. Hist.,’
vol. x, 1852.--_Idem_, “Helminthology,” trans. by Busk and pub. in ‘Ray
Soc. Rep. on Zool.,’ 1843-44, p. 446, London, 1847.--_Idem_, “On the
Transformation of _Cysticercus pisiformis_ into _Tænia serrata_,” from
‘Zeitsch. f. w. Zool.,’ in ‘Quart. Journ. Micr. Sci.,’ 1854.