NEW ASEXUAL TAPEWORM. 



843 



network of the latter. I could find no trace of this in the sexual 

 worm, although it was easy to see in the supposed Oysticercoid of 

 the same. It seems to me possible (perhaps necessary) to explain 

 this difi'erence by assuming in the Cysticercoid a retention and 

 gradual metamorphosis of the bladder into the strobila, together 

 with its excretory system, which latter ultimately disappears on 

 the assu.mption of sexual characters. There are, of coixrse, other 

 Cestodes in which the bladdev is not cast off before the acquiring 

 of sexual characters. 



Text-fig. 119. 



Part of a transverse section through a proglottid of the sexual worm. 



cm. Circular muscles, d.v. Dorsal vessel of the water vascular system. N. The 

 three lateral!}' running nerve-cords, t.v. Transverse water vascular trunk, 

 v.v. Ventral trunk. X. Large longitudinal muscular fibres referred to in the 

 text as frequently running within a space. 



In the neighboiirhood of the water vascular trunks delicate muscular fibres are 

 shown running chiefly in a dorso-ventral direction, which may be associated with 

 the dilation and contraction of the water vascular tubes. 



The nerve-cord shows no trace of the asymmetry which I have 

 described above in the very young worms. There is nothing un- 

 usual about the position or structure of the main trunks. There 



