184 EoBEET Thompson Young, 



zation, which have been so warmly disputed in the past, it is 

 necessary, not merely to study in detail many and varied adult 

 forms, but also to make an exhaustive study of the development of 

 the larva in its finer details. Thus far no thoro investigation 

 has been made along this line, tho there are a few papers dealing 

 with the histogenesis of différent organs in the adult tapeworm, and 

 some histogenetic details have appeared incidentally in various 

 articles concerned primarily with other lines of investigation, viz.: 

 Bdgge (1902), Lung WITZ (1895) and Schmidt (1888). From my study 

 of a considerable number of larvae in all stages of development 

 I hope to throw some light on this hitherto neglected subject. 



It may as well be stated at the outset that, wherever there has 

 been occasion in what follows to dispute the statements of other 

 authors, this is always done with the reservation that such objections 

 apply only to Cysticercus pisiformis', unless the contrary is 

 expressly stated. While it is very probable that the tissues of this blad- 

 der worm agree closely with those of other Cysticerci and Taeniae 

 still no such comprehensive statement can be made. 



2. Materials and Methods. 



Cysticercus pisiformis occurs in great numbers in the 

 cottontail rabbit (Lepiis mearnsi) in the vicinity of Lincoln. Of 

 50 rabbits examined, 34 were infected. In 21 infected rabbits the 

 total number of larvae present was 227, making an average of 10,8 

 larvae to each rabbit.^) The older larvae occur almost exclusively 

 in the body cavity and chiefly along the rectum, just dorsal to the 

 symphysis pubis, occasionally free, but mainly enclosed in con- 

 nective tissue cysts, which usually contain only a single larva, but 

 occasionally two or even three, while Schaaf (1905) states that he 

 has found 18 larvae of Cysticercus pisiformis in one cj^st. 



In addition to those larvae obtained from market rabbits, all 

 of which were in well advanced stages of development, a large num- 

 ber of larvae in the earlier stages of development were obtained 

 by means of feeding experiments. In each of these the proglottids 

 of Taenia serrata were used. 



1) It is possible that in some of these rabbits there were very small 

 larvae present and uncounted in some of the organs. There was no 

 evidence of this, however. 



