

CHAPTER IV. 



ON THE ORIGIN OF THE CESTOID AND CYSTIC ENTOZOA. 



THE extraordinary likeness of the Cysticercus fasciolaris of 

 rats and mice with the Ttenia crassicollis of cats, and the fact 

 that the above rodents are the principal food of cats, and that, 

 moreover, the joints of the Cysticercus fasciolaris enclosed in the 

 cysts in the livers of rats and mice are never sexually developed, 

 inclined me to helieve that this sexless Cysticercus fasciolaris 

 would be changed into a sexually matured Tcenia crassicollis, as 

 soon as the animal it lodged in should be devoured by a cat. 

 For, under these circumstances, the liver of the devoured rodent 

 would be digested in the cat's stomach, and the cystic worm, 

 freed from its cyst, would be transplanted to a place where, after 

 casting off its caudal vesicle, it might, as a Tcenia crassicollis, 

 attain to sexual maturity in the intestine of the cat. Fully as I 

 was persuaded of the possibility of such a transformation of the 

 Cysticercus fasciolaris into Tania crassicollis, yet I could hardly 

 conceive that the other species of Cysticercus, in which no jointed 

 body was developed between the head and caudal vesicle of the 

 scolex, could become Taeniae ; and this appeared the more un- 

 likely, as I had often found cysts that had perished, in which the 

 Cysticerci they contained were dead, and lay shrunk and buried 

 amidst inorganic calcareous deposits. Such a calcareous de- 

 generation of the cysts 1 must assuredly render the cestoid scolices 

 incapable of propagation -, still all do not meet with this fate, for 

 under favorable circumstances they can, even in spite of their 

 dropsical receptacle, subserve the multiplication of sexual cestoids ; 

 that is to say, when they are transported into the intestinal canal 

 of animals fitted for the development of Proglottides. 



That the cystic Entozoa can thus become changed into sexual 



1 I have mor3 particularly described this process in the 'Zeitscrift fiir Wissenschaft- 

 liche Zoologie,' Bd. ii, 1850, p. 225. 



