126 



ZOOLOGY 



separated from the intestine by a slight constriction. 

 The latter is often flattened dorso-ventraUy, 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 



Fig. 82.- 



-Transverse section through about the middle of the body of Ascaris. 

 Slightly diagrammatic. 



1. Dorsal median nerve. 



2. Ventral median nerve. 



3. Cuticle. 



4. Hypodermis, a granular layer. 



6. Muscle-cells, the striated outer border. 



6. Muscle-cells, the granular nucleated 

 inner part. 



10, 



Accumulation of granular protoplasm 



round — 

 Lateral excretory canals. 

 Intestine. 

 Uterus with eggs. 



11. Ovarian tubules. 



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 



