immADM. 113 



attained a lengtli of several lines, but if examined microscopically 

 the head will still be found to be imperfectly formed. Their 

 perfect cysticercal state is acquired only after undergoing a second 

 process of encystation, which is usually completed at the expira- 

 tion of eight weeks. 



The various parts of the head successively appear after the 

 same fashion as the head itself. Cloudy masses of closely aggre- 

 gated cellules collect here and there, i.e., in places specially 

 destined to develop the suckers, the coronet of hooks, and other 

 parts. The receptaculum capitis becomes thinned out and dis- 

 placed by the neck and folds of the (subsequent) body, both of 

 which regions make their appearance whilst the head is yet 

 enclosed in the receptaculum. The head afterwards becomes 

 included within the folds of the body, and the whole mass is 

 eventually protruded from the surrounding caudal vesicle, at the 

 pleasure of the animal. At this period of their complete develop- 

 ment, the Cysticerci begin to degenerate and calcify, when not 

 transferred to their proper final " host." 



It has been abundantly proved that the administration of 

 Cysticerci which have only arrived at their wandering (imperfect 

 larval) condition will produce only negative results, whilst those 

 which have undergone a second encystation — or, in other words, 

 are eight weeks old — will, in the intestine of their appropriate final 

 host, readily develop into the Tmnia serrata.* If the mature 

 larv£e are enclosed in stout investing capsules at the time of their 

 passive introduction into the dog's stomach, several hours may 

 elapse before the cysts will be digested ; but, if the envelopes be 

 thin, two or three hours will sufi&ce, not only to remove the adven- 

 titious coverings, but also to destroy the caudal vesicle of the Cys- 



* I have administered to dogs upwards of thirty fresh immature specimens of Cysticer- 

 cuspisiformis, in five separate worm-feedings, but in no case have these larvae been able 

 to undergo further development. On the other hand, I have, on four occasions, fed 

 dogs with several mature examples of the same Cysticercus, and in every instance I 

 have succeeded in procuring the Tcenia serrata. In one instance only was there any doubt 

 in my mind as to the success of the breeding-experiment. — T. S. C. 



Q 



