256 



ZOOLOGY 



SECT. 



to each of these bothridia, which, by coalescence, may appear to be 

 reduced to two, may be a small sucker of the ordinary kind. In 

 Tetrarhynclms (Fig. 206) there are four very long and narrow 

 rostella, or " proboscides," covered with hooklets, and capable of 

 being retracted into sheaths. 



The Cestoda are devoid of mouth, and in most of them the 

 genital apertures are marginally placed, so that, externally, there 



is - - except in 

 the case of a 

 few in which the 

 genital apertures 

 are not marginal 

 nothing to dis- 

 tinguish the dor- 

 sal surface from 

 the ventral. The 

 body, or strobila, 

 which is nar- 

 rower in front 

 than it is 

 further back, 

 is made up 

 throughout its 

 length of a series 

 of segments, or 

 p roglottides, 

 which become 

 larger and more 

 distinctly 

 marked off from 

 one another as 

 we pass back- 

 wards. Tcenia 

 e chin o coccus 

 (Fig. 207) is 

 exceptional in 

 possessing only 

 three or four 

 proglottides. In 

 a few (Ligula 

 and its allies 



Fig. 208), though the body has the normal elongated ribbon-like 

 form, the segments are not distinct, and in CaryophyllcBus (Fig. 209), 

 Amphilina, Gyrocotyle (Amphiptyches Fig. 210), and Archigetes 

 (Fig. 211) (which is perhaps merely a young stage of Caryo- 

 phyllcBUs), segmentation is entirely absent, the whole body in 

 these genera consisting of a single proglottis. The surface in 

 the Cestodes is devoid of cilia, and there is no pigment. 



FIG. 205. Actinodacty lella. b. c. bursa copulatrix ; br. brain ; 

 c. penis ; t. intestine ; oo. ovary ; ph. pharynx ; T. v. receptacu- 

 lum ; s. sucker ; t., t. testes ; ut. uterus ; v. vitelline glands ; 

 v. s. vesicula seminalis. 



