784 PAEASITIC DISEASES. 



with its head and segments. The ripe segments containing the 

 eggs detach and get out of the body, and now the eggs are again 

 ready to commence anew their life cycle. 



The development of the Bothriocephalus differs in several 

 respects from that of the Tccnia. The egg-shell is provided with 

 a lid. In its interior the embryo is formed, the outer layer of 

 cells forming the ciliated coat, and the central mass of cells the 

 six-hooked embryo. The ciliated embryo comes out of the shell 

 by the opercular aperture, and by means of its cilia swims about 

 in the water. Experiments have shown that the embryos of 

 Bothriocephalus latus can develop into a sexually mature worm 

 without passing through a cystic stage. The eggs were taken 

 and kept for six months in fresh water till the embryos were 

 formed. A very young pup was supplied with milk containing 

 these eggs and the ciliated embryos. On the 10th July the 

 pup was fed with the eggs, and on the 25th August it passed a 

 Bothriocephalus latus 42| cm. long, — that is, about 17 inches. 

 On the 9th September it was killed, and three Bothriocephcdi 

 were found in its intestines. 



Interesting as are the phenomena connected with the origin 

 and development of the various tape- worms found infesting our 

 domesticated animals, it is not necessary for the practitioner of 

 veterinary medicine to acquaint himself with the natural history 

 details of all the forms which are apt to come under his notice ; 

 nevertheless he will find it useful to have a general knowledge 

 concerning some of them. Thus, he should know that no less 

 than six different kinds of tape-worm infest the dog. Of these, 

 he should be further aware that one {Tcenia serrata) is acquired 

 by swallowing the larvae {Cystieercus pisiformis) which reside in 

 the bodies of rabbits and hares; that another {Tccnia mar- 

 ginata) is obtained by devouring the larvce [Cysticcrcus teiiuicollis) 

 which reside in the viscera of the sheejD and pig ; that another 

 {Tcenia ccenurus) is obtained by ingesting the larvae (Ccenurus 

 ccrehralis) which infest the brains of sheep and other animals ;. 

 that another {Tccnia echinococcus) is developed when the dog 

 swallows the larvae {Echinococcus veterinorum) found in the 

 viscera of various animals, especially the pig ; and lastly, that 

 yet another {Tcenia cucumerina) results from swallowing the 

 dog louse {Trichodcetes latus), which harbours its representative 

 cysticercus or measie. 



