280 



ZOOLOGY 



SECT. 



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. son.'), which opens 

 by a short, narrow muscular tube, the 

 ductus ejaculatorius, into the rectum. 

 Behind the rectum, and opening into its 

 dorsal wall, are paired muscular sacs (s.}, 

 containing the penial sctcc (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 110 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 <:ili. 



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 (nig.} 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 in a chitinoid egg-shell, and are passed out of the body 

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

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



i;. I'iG. Diagram of Xervous 

 system of Xeniatoda. c. 

 commissures ; ill,,, .[nrs.-tl 

 nerve : lisa, ivisteriipr Literal 

 nerve; o. n. upper and i*,!. 

 under portion of nerve- 

 ring ; s. ri. lateral swellings ; 

 ,-l:i. ventral nerve. (From 

 Lang, after Biitschli.) 



