The Histogenesis of Cysticercus pisiformis. 195 



different preparations and in different parts of the same preparation, 

 undoubtedly traceable to local differences in density. In view of 

 this fact and of the continuous network of fibres traversing the 

 developing cuticula, I hesitate to separate the inner layer into two, 

 the basal of which shall represent a region in which the processes 

 of the sub-cuticular cells terminate. 



The Hooks. Regarding the development of these structures, 

 but little can be added to the account given by Leuckart (1856: 

 137). Especial attention should be paid, however, to the fact that 

 the hooks are developed "als lokale Entwicklungen derselben (Epi- 

 dermoidalauskleidung des Hohlraumes)". In the developing hooks 

 represented in Fig. 17, the continuity of the cuticular fibrillae with 

 the base of the hooks shows very clearly that the latter are formed 

 by a binding together of the former with an inlaid cement sub- 

 stance similar to the development of the cuticula itself. I agree 

 with the majority of previous authors in regarding the hooks as 

 cuticular structures. They are not, however, directly cel- 

 lular products, but rather are derived from par- 

 enchyma fibrillae. I cannot in any sense agree with the view 

 of Beaux (1894—1900: 1238) that "diese Bildungen müssen von den 

 über die Cuticula hervortreten sollenden Protoplasmafäden (wenn 

 solche überhaupt existieren) wohl unterschieden werden". 



A considerable part of the outer layer of the cuticula of the 

 head cavity at an early stage presents small filiform or conical 

 deeply stained processes varying greatly in size. A few of these 

 processes magnified 1000 times are shown at h', Fig. 17. This figure 

 shows their great variations in size. It also shows that, like the 

 hooks, they are composed of bundles of fibrillae. In fact, these pro- 

 cesses are primitive hooks, which are cast off from time to time 

 during the growth of the cuticula. 



I am unable to corroborate the statements of Leuckaet (1856) 

 regarding the origin of the base of the hooks as a separate devel- 

 opment. I have examined the developing hooks in eleven larvae 

 and in only two of these have I seen anything to suggest a sepa- 

 rate origin of the body and base of the hooks (see Fig. 9). In the 

 majority of cases the base develops directly in continuity with the 

 body of the hook. Leuckart gives no figures which support his 

 statements and consequently I am at a loss to compare his state- 

 ments with my own. 



