Parasites from the Zoological Gardens. 347 



PARASITES FROM THE ZOOLOGICAL GARDENS. 



BY T. SPENCEK COBBOLD, M.D V E.L.S., 



Lecturer on Comparative Anatomy, Zoology, and Botany, at the Middlesex 



Hospital Medical College. 



Having during the four successive winters of 1857 — 60, in- 

 clusive, examined the carcasses of upwards of one hundred 

 different species of vertebrata dying at the Zoological Society's 

 Menagerie, Regent's Park, we are enabled to form a tolerably 

 accurate estimate of the prevalence of entozoa in animals sub- 

 jected to a condition of domesticity as compared with those 

 living in a wild state. It is, we believe, very commonly sup- 

 posed that tame quadrupeds and other beasts kept " cribbed, 

 cabined, and confined/' are much more troubled with parasites 

 than those fortunate individuals who roam at large " o'er hill 

 and dale " without any human being to molest them. This 

 conclusion, in so far as external parasites are concerned, may 

 possibly be true (which, by the way, however, we very much 

 doubt), but, as regards the frequency of internal parasites, we 

 have satisfied ourselves as to the erroneousness of the general 

 belief. About one-third only of the birds, reptiles, and quadru- 

 peds just enumerated were found infested, or thirty-eight species 

 in all; and of these, nineteen were mammals, fourteen were 

 birds, and five were reptiles. This is decidedly a small pro- 

 portion, and the comparative scarcity of the parasites is espe- 

 cially marked when we limit the question of their number with 

 particular reference to the presence or absence of the members 

 of that remarkable group of entozoa which we call flukes. In 

 all our carefully conducted examinations we have only found 

 seven different kinds of flukes, or trematodes, as they are more 

 scientifically called ; and as some of these offer interesting types 

 of structure, and at the same time give rise to curious sugges- 

 tions, it accords with our present purpose to offer a more or 

 less brief account of each of them, omitting such details as 

 are interesting merely to systematists. It may be premised, 

 however, that a true explanation of the cause of this com- 

 parative freedom from flukes, which the animals in the 

 Society's menagerie appear to enjoy, arises out of the circum- 

 stance that the larvae, of Trematodes exist only in a limited 

 number and kind of molluscan hosts, and consequently qua- 

 drupeds, and other vertebrates from foreign lands, are not so 

 liable to swallow the larvae suitable to themselves, seeing that 

 the larvae frequently exist in molluscs, and in other hosts, which 

 are not to be found in this country. No doubt, as in the case 

 of the Fasciola hepatica, some trematode parasites will take 



