170 PARASITOLOGY. 



CESTODA. 



The order Cestoda (kestos — girdle, eidos — like) 

 belongs to the class Plathelmintha and includes a 

 large group of worms that are provided with a ribbon 

 shaped body, proceeding from a small head and 

 neck. The head or scolex may be provided with 

 four sucker discs and a rostellum of booklets. The 

 booklets are arranged in two circular rows in the 

 center of a square formed by the four sucker discs 

 at the extreme cephalic extremity. This is called an 

 armed taenia (tapeworm). The head may be pro- 

 vided with only four sucker discs. This is called an 

 unarmed taenia. These constitute its fixation ap- 

 paratus by which means it fixes itself firmly to the 

 mucous membrane of the intestine and floats back in 

 the intestinal contents. A neck connects the head 

 with the body; in some species it is short, in others 

 long and slender, while in others, as the species 

 found in the horse, the neck is absent. The body is 

 fiat, ribbon-shaped and segmented ; it is composed 

 of a network of cells with anastomosing prolonga- 

 tions. The integument comprises a homogeneous 

 cuticle lying on a subcuticular layer of longitudinal 

 and transverse fibers. It is provided with a rudi- 

 mentary nervous system which consists of two long- 

 itudinal cords united by a transverse commissure at 

 the head. There is no digestive apparatus ; the 

 worm absorbs nourishment through fine canaliculi 

 which traverse the cuticle. There is no circulatory 

 apparatus ; the integument serves for the exchange of 

 gases. The excretory canal consists of four tube- 

 like structures which traverse the entire length of 



