ANATOMY OF THE CESTODA 



2 9 I 



(fig. 184, PL) ; they lie internal to the subcuticular cells and, piercing the 

 cuticle with their peripheral processes, end as projecting " receptor " 

 hairs. Higher organs of sense are not known. 



The EXCRETORY APPARATUS of the Cestodes is similar to that of 

 other flat worms. The terminal 

 (flame) cells, which hardly differ 

 in appearance from those of 

 the Trematodes, are distributed 

 throughout the parenchyma, but 

 are more common in the cor- 

 tical than in the medullary layer 

 (fig. 184, T.c.). Before opening 

 into a collecting tube, the capil- 

 laries run straight, tortuously, 

 or in convolutions, anastomos- 

 ing frequently with one another 

 or forming a rete mirabile. The 

 collecting tubes, which have 

 their own epithelial and cuti- 

 cular 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. 189) ; they lie side by side, 

 two (a wider thin-walled ventral, 

 and a narrower thick-walled 

 dorsal one) in either lateral field ; 

 in the head the two vessels on 

 each side unite by means of a loop, at the posterior extremity they 

 open into a short pyriform or fusiform terminal bladder which dis- 

 charges in the middle of the posterior edge of the original terminal 

 proglottis. 



This primitive type (fig. 189) of arrangement of collective tubes is 

 subject to variation in most Cestodes, in the scolex as well as in the 

 segments. Indeed, even the lumen of the four longitudinal tubes 

 does not remain equal, as the dorsal or external tubes are more fully 

 developed and become thicker, whereas the ventral or internal ones 

 remain thin, and in some species quite disappear in the older seg- 

 ments (figs. 185, 187). Moreover, very frequently connections are 

 established between the right and left longitudinal branches, as in the 

 head, where a " frontal anastomosis" develops, which in the Tceniidcx 

 usually takes the form of a ring encircling the rostellum (fig. 190), and 

 in the segments of a transverse anastomosis at each posterior border, 



FIG. 188. Tcenia canurtts, head and part of 

 neck showing nervous system. Enlarged. (After 

 Niemiec.) 



