VI 



PHYLUM NEMATHELMINTHES 



297 



the rectum. Behind the rectum, and 

 opening into its dorsal wall, are paired 

 muscular sacs (s.), containing the penial 

 setce (pn. s.) already noticed. The anterior 

 end of the testis consists of a solid mass of 

 sex-cells ; passing backwards there is 

 found a cord or rachis occupying the axis 

 of the tube and having the sperm-cells 

 attached to it ; still further back the 

 sperms become gradually differentiated, 

 and are finally set free in the vas deferens. 

 The sperms are peculiar rounded cells 

 (Fig. 23, p. 31, c. d. e.) ; when transferred 

 into the body of the female they exhibit 

 amoeboid movements, but as long as they 

 remain in the male ducts they are non- 

 motile : they have no trace at any stage 

 of the characteristic tail of the typical 

 sperm. In this connection it may be 

 mentioned that the tissues of Ascaris are 

 remarkable for the total absence of cilia. 



The organs of the female (Fig. 245) re- 

 semble those of the male, but are double 

 instead of single. There are two coiled, 

 thread-like ovaries (ovy.), each passing in- 

 sensibly into a uterus (ut.). In the ovary, 

 as in the testis, the eggs are developed 

 in connection with an axial cord or rachis. 

 The two uteri unite in a short muscular 

 vagina (vag.) which opens, as already seen, 

 on the ventral surface of the body (gnp.) 

 at about one-third of the entire length 

 from the head. 



Development. The eggs are pro- 

 duced in immense numbers at the rate, 

 it has been reckoned, of about 15,000 a 

 day. They are fertilised in the upper 

 part of the uterus, each becoming enclosed 



-din 



-han 



FIG. 246. Diagram of ner- 

 vous system of Nematoda. 

 c. commissures ; din. dorsal 

 nerve ; few. posterior lateral 

 nerve ; on. upper aud un. 

 under portion of nerve- 

 ring ; s.g. lateral swellings ; 

 vln. ventral nerve. (From 

 Lang, after Biitsehli.) 



rtl.f 



Fio.^247. Ascaris lumbricoides, posterior extremity of male, 

 dissected, an. anus ; cu. cuticle ; der. epthm. epidermis ; m. 

 muscular layer ; pn.s. penial seta ; s. sac containing penial seta ; 

 is. testis : vs. sem.' vesicula semlnalis. 



