428 The Animal Kingdom 



body, the intestine narrows to the short rectum, which opens through 

 the anus. In the male, a portion of the rectum serves as a cloaca for 

 the reception of both sperm and waste food materials. 



By special staining techniques, the nerve ring surrounding the 

 pharynx and some of the nerves leading from it can be demonstrated. 

 Excretion of metabolic wastes is by means of a series of excretory 



tubes. 



The female worms possess a single ovary which is posterior to the 

 mid-point of the body. Continuous with the ovary is an oviduct and 

 uterus. The uterus merges into the vagina which opens out at the 

 vulva in the posterior portion of the body. The eggs develop into larvae 

 within the uterus, and are liberated by the rupture of the body. 



DO«SAL NERVE 



MUSCLE CELL 

 PROCESS 



INTESTINAL 

 EPITHELIUM 



PSEUDOCOEL 



VENTRAL NERVE 



Fig. 140. — Cross section of the nematode, Ascaris. 



The male has but a single elongate testis and a vas deferens for the 

 conduction of sperm. The posterior end of the vas deferens is modified 

 to form the serninal vesicle for storage of sperm. Posterior to the 

 seminal vesicle is the ejaculatory duct which joins the rectum to form 

 the cloaca. The cloaca is provided with two copulatory spicules, ac- 

 companied by an accessory piece, the guhernaculum. 



A cross section of the worm illustrates the general relationships 

 of the internal structures. The body essentially consists of two con- 

 centric tubes : one is the outer body wall, the other the digestive tract. 

 The body wall is relatively thick, consisting externally of the heavy, 

 noncellular, striated cuticle. Beneath this is a thin layer of syncytial 

 cells, the hypodermis, and beneath these cells are the spindle-shaped 

 longitudinal muscles. Dorsally and ventrally nerve cords are visible; 

 laterally a median projection of the lateral line carries the excretory 



