126 ZOOLOGY 
separated from the intestine by a slight constriction. 
The latter is often flattened dorso-ventrally, it possesses no 
intrinsic muscles, and is lined by a layer of columnar cells 
(Fig. 82). On both the outside and the inside of the canal is 
a thin cuticle, apparently secreted by the columnar cells, and 
the internal cuticle is perforated by a number of minute pores. 
The rectum is of smaller diameter than the intestine, its walls 
contain muscle-fibres ; in the male the vas deferens opens into 
it, and its posterior end thus forms a cloaca (Fig. 81). 
There is no vascular system in Nematodes. The excretory 
system consists of two tubes, which run along the lateral line 
Fic, 82.—Transverse section through about the middle of the body of Ascaris. 
Slightly diagrammatic. 
1. Dorsal median nerve. 7. Accumulation of granular protoplasm 
2. Ventral median nerve. round— 
3. Cuticle. 8. Lateral excretory canals. 
4, Hypodermis, a granular layer. 9. Intestine. 
5. Muscle-cells, the striated outer border. 10. Uterus with eggs. 
6. Muscle-cells, the granular nucleated 11. Ovarian tubules. 
inner part. 
of the animal, separating the longitudinal muscles of each side 
into a dorsal and a ventral portion (Fig. 82). Almost a third 
of the body-length from the anterior end these two canals give 
