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 hooklets. The 
hooklets 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 
flat, 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 
