194 



THE ANIMAL PARASITES OF MAN 



like manner (fig. 122). Every change in the bending of the 

 surface of the rostellum induces an alteration in the position of 

 the hooks. In the hookless taeniadae the muscular system of the 

 rostellum is altered in a very different manner ; in a few forms 

 a typical -sucker appears in its place. 



The NERVOUS SYSTEM commences in the scolex and runs through 



the neck and the entire series of 

 proglot tides. Within the prog- 

 lottides it consists of a number 

 of medullary fasciculi running 

 longitudinally, and of which 

 those at each lateral border are 

 usually the most powerful. In 

 the tcenke the lateral fasciculi 

 are accompanied both dorsally 

 and ventrally by a thinner fasci- 

 culus (concomitant fasciculus 

 (fig. 1 1 9); on each surface, more- 

 over, between the lateral fasci- 

 culi and the median plain, there 

 are two somewhat stronger fas- 

 ciculi (sub-median fasciculi), so 

 that there is a total of ten 

 longitudinal fasciculi. They 

 lie exteriorly to the trans- 



FIG. 122. Longitudinal section of the head verse muscle plates, and the 



and neck of Tcenia crassicollis. 30/1. Lm., 

 longitudinal muscles of the neck; Lf., lat- 

 eral fasciculi ; G., ganglion ; Sc., subcutic- 

 ular layer; W r , external; TJ^., interior ex- 

 cretory vessel. 



lateral and concomitant fas- 

 ciculi lie exteriorly to the 

 principal excretory vessels, and 

 are everywhere connected by 



numerous anastomoses which again anastomose ; one typical annular 

 commissure is usually found at the posterior border of the seg- 

 ments. In the Bothriocephalidae the distribution of the fasciculi is 

 different (for instance, two lie in the medullary layer), or they are 

 split up into a larger number of branches. In the scolex the 

 fasciculi are connected in a very remarkable manner by commis- 

 sures with that which is generally termed the central part of the 

 entire nervous system. There occurs normally a commissure 

 between the two lateral fasciculi, at the same level, and the 

 dorsal and ventral median fasciculi are also connected AT EACH 

 SURFACE as well with each other as with the lateral fasciculi, so 

 that a hexagonal or octagonal figure is formed. The so-called apical 



