302 



ZOOLOGY 



SECT. 



din 



its ventral portion (un.) is thickened and ganglion-like. The only 

 sense-organs are little elevations, the sensory papilla (Fig. 237, p.), 

 on the lips. 



The reproductive organs are formed on a peculiar and very 

 characteristic pattern. The testis (Fig. 242, ts.) is a long, coiled 

 thread, about the thickness of fine sewing- 

 cotton, and occupying a considerable por- 

 tion of the body-cavity. At its posterior 

 end it is continuous with the vas deferens, 

 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 ejaculatorius, into the rectum. 

 Behind the rectum, and opening into its 

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

 containing the petiial setce (pn. s.) already 

 noticed. The anterior end of the testis con- 

 sists 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. 30, 

 c. d. e.) ; when transferred into the body 

 of the female they exhibit amoeboid move- 

 ments, but as long as they remain in the 

 male ducts they are non-motile : they 

 have no trace at any stage of the char- 

 acteristic 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. 240) 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. 



-Jum 



FIG. 241. Diagram of nervous 

 system of Nematoda. c. 

 commissures ; din. dorsal 

 nerve ; hsn. posterior lateral 

 nerve ; on. upper and un. 

 under portion of nerve- 

 ring ; s. g. lateral swellings ; 

 vln. ventral nerve. (From 

 Lang, after Btttechli.) 



