CESTODES : EXCRETORY ORGANS 



195 



nerves pass from this commissural system anteriorly, embrace the 

 secondary muscular system of the rostellum semi-circularly, and 

 form an annular commissure (rostellar ring) at the inner part of 

 the rostellum. 



The peripheral nerves arise from the fasciculi, as well as from 

 the commissures situated in the scolex ; some go direct to the 

 muscles, while others form a close plexus of nerves from the inner 

 to the outer longitudinal muscles, which plexus likewise sends out 

 fibres to the muscles, but principally to numerous fusiform organs 

 of sense (fig. 118, PI.) ; they pass between the subcuticular 

 cells and reach the cuticle with their peripheral processes, there 



FIG. 123. Young Acanthobothnum 

 coronatum, v. Ben... with the excretory 

 vessels outlined ; slightly enlarged. 

 (After Pintner.) 



FIG. 124. Scolex of a cysticer- 

 coid from Arion, with the excre- 

 tory vessels outlined. (After 

 Pintner.) 



finishing with a small terminal plate. Higher organs of sense are 

 not known. 



The EXCRETORY APPARATUS of the cestodes is similar to that of 

 other flat worms. The terminal cells, which hardly differ in appear- 

 ance from those of the trematodes, are distributed throughout the 

 parenchyma, but are more common in the cortical than in the 

 medullary layer (fig. 118, Ts.). Before reaching a collecting tube, 

 the capillaries run straight, tortuously, or in convolutions, they greatly 

 anastomose with one another or form rete mirabile. The collecting 

 tubes, which have their own epithelial and cuticular wall, and which 

 also appear to be provided with muscular fibres, occur typically as 

 four canals passing through the entire length of the worm (fig. 123), 

 they lie side by side, two on either lateral border ; in the head the two 

 vessels on each side unite by means of a loop, at the posterior ex- 

 tremity they open into a short pyriform or fusiform terminal bladder 



