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 lavre within their vital organs. 
“The herbivorous animals and ourselves get the 
echinococcus disease by swallowing ne eggs of the hydatid 
tapeworm. 
“Fig. 29, A, is a representation of the parasite. It ex- 
hibits the head-segment with its four suckers, and crown of 
hooks (a), and three ordinary segments (4, ¢, 2), 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 may have 
thousands of tapeworms all resulting from a solitary germ.” 
He thus explains it : 
“ Eggs escape from the dog fer anum. One swallowed 
by any herbivorous animal, say a shéep, 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 tenia-like crown of 
hooks (a), the suckers (0), the calcareous particles (c), and 
a vesicular body (ay. 
‘“* When, therefore, a dog is fed on the viscera of a sheep 
containing perfect 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 
