WORMS. 329 



It would be an endless labour to expatiate 

 in this vast field where the rest of the animal 

 kingdom is concerned, amidst therefore the 

 various and strange forms that are destined to 

 this office, I shall select only a few, beginning 

 with one that affects one of the most valuable 

 of our animal possessions, I mean the Hydatids, 1 

 which particularly and often fatally affect our 

 flocks of sheep, not indeed that they are con- 

 fined to them, for they are found also in swine, 

 deer, and oxen, and even in man himself. 



These animals resemble the tape-worm in 

 their oral organs, but their body, especially 

 posteriorly, is vesicular. The lymphatic vesicles 

 are what medical men call hydatids ; they are 

 found usually in the brain and in the liver 

 of these animals. Their size varies according 

 to the species, some are as big as the fist, 

 and one was shewn to the School of Medicine 

 in Paris as big as a man's head. Their shape 

 varies, but generally is somewhat spheroidal, 

 their substance is composed of membranes one 

 on another more or less thick, and formed of 

 circular fibres visible only under a lens ; they 

 are half- filled with transparent lymph. They 

 exhibit a peristaltic motion which is often very 

 lively. 



Three species more particularly annoy our 

 sheep. The cerebral hydatid, 2 which finds its 



1 Hydatis. ~ H. cerebralis. 





