PHYLUM NEMATHELMINTHES 



171 



The male reproductive organs are a single, coiled thread-like 

 testis, from which a vas deferens leads to a wider tube, the seminal 

 vesicle; this is followed by the short muscular ejaculatory duct 

 which opens into the rectum. In the female lies a Y-shaped 

 reproductive system. Each branch of the Y consists of a coiled 

 thread-like ovary (Fig. in, 3) which is continuous with a larger 

 canal, the uterus (4). The uteri of the two branches unite into 

 a short muscular tube, the vagina (5), which opens to the outside 

 through the genital aperture (6). Fertilization takes place in 

 the uterus. The egg is then surrounded by a shell of chitin, and 



Fig. 112 a. — Parts of Ascaris lumbricoides. a, hind end of male with the 

 two penial seta? (Sp). b, anterior end from the dorsal side, showing the dorsal 

 lip with its two papilla?, c, the same from the ventral side with the two lateral 

 ventral lips and the excretory pore (P). d, egg with external membrane of 

 small clear spherules. (From Sedgwick, after Leuckart.) 



passes out through the genital pore. The chitinous egg-shell 

 prevents the digestion of the egg within the intestine of the host. 



The relations of the various organs to one another, as well 

 as the structure of the body-wall, and the character of the ccelom, 

 are shown in Figure 112b, which is a transverse section of a female 

 specimen of Ascaris lumbricoides. The body of the worm should 

 be considered as consisting of two tubes, one the intestine (int.), 

 lying within the other, the body-wall; while between them is a 

 cavity, the ccelom, in which lie the reproductive organs (ovy. 

 and ut). 



The body-wall is composed of several layers, an outer chitinous 

 cuticle (cu), a thin layer of ectoderm (der.epthm) just beneath it. 



