280 



ZOOLOGY 



SECT. 



din 



able portion of the body-cavity. At its posterior end it is con- 

 tinuous with the vas defcrens, the two passing insensibly into one 

 another so that the junction is not visible externally. The vas 

 deferens, in its turn, becomes continuous with a wide canal, the 



vesicula seminalis (vs. sem.), which opens 

 by a short, narrow muscular tube, the 

 ductus cjacidatorius, into 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. 20, p. 

 28, 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 remark- 

 able for the total absence of cilia. 



The organs of the female (Fig. 225) 

 resemble those of the male, but are 

 double instead of single. There are two 

 coiled, thread-like ovaries (ovy.), each pass- 

 ing insensibly 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 (vctg.) which 

 opens, as already seen, on the ventral 

 surface of the body (ffnp.) 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 in a chitinoid egg-shell, and are passed out of the body 

 of the host with its fyeces. Segmentation is complete, but the 

 details of development are not known in this species, neither is 



FK;. 2'2G. Diagram of Xervous 

 system of Nematoda. c. 

 commissxires ; <!(n. dorsal 

 nerve ; /<./. posterior lateral 

 nerve; o. n. upper and vm. 

 under portion of nerve- 

 ring ; s. (i. lateral swellings ; 

 vln. ventral nerve. (From 

 Lang, after Biitschli.) 



