Internal Parasites. 231 



in the juvenile stages of growth. To be sure, its bad 

 effects are chiefly witnessed in the human subject; but 

 cattle, sheep, horses, and swine occasionally perish from 

 the presence of the lavrae within their vital organs. 



" The herbivorous animals and ourselves get the 

 echinococcus disease by swallowing the eggs of the hydatid 

 tapeworm. 



"Fig. 29, A, is a representation o( the parasite. It ex- 

 hibits the head-segment with its four suckers, and crown of 

 hooks {a), and three ordinary segments {b, c, d), the lower- 

 most of which is sexually mature, displaying numerous 

 eggs internally. Water-vessels traverse the entire length 

 of the worm. 



One of the strangest points connected with this entozoon 

 is the extraordinary provision made for its propagation. In 

 ordinary cases one tapeworm only results from the growth 

 of the products of a single egg ; but here we inay have 

 thousands of tapeworms all resulting from a solitary germ.'' 



He thus explains it : 



" Eggs escape from the dogger anum. One swallowed 

 .by any herbivorous animal, say a sheep, will (by a 

 lengthened process of development, the details of which I 

 need not give) eventuate in the formation of hydatids. 

 These hydatids, under favourable circumstances, will by 

 internal budding produce innumerable heads or scolices 

 (Fig. 29, B), each of which display the taenia-like crown of 

 hooks («), the suckers {b), the calcareous particles (c), and 

 a vesicular body (a). 



" When, tjierefore, a dog is fed on the viscera of a sheep 

 containing perfert hydatids of this description, all the 

 numerous heads become developed into tapeworms in the 

 animal's intestines. This has been proved over and over 

 again by experiment. 



" Most of the heads are developed in delicate sacs, termed 

 brood-capsules, one of which is here represented in the col- 

 lapsed or broken-up state (Fig. 30). It will be further 



