VI 



PHYLUM NEMATHELMINTHBS 



315 



suspensory ligament. From each a vas rlefeivn.s (v. df.), furnislied with several 

 nikuhe ■^cmlini/ei or sacs for the storage of spermatic fluid, passes Imckwards 



Fu;. 253. — A, longitudinal section through the terminal twigs of the nephridia of Echino- 

 rbyncbus gigas ; highly magnified, a, nucleus. B, a tcmiinal twig more highly magni- 

 fied, b, the porous membrane. (From Shipley, after Kaiser.) 



and unites witli its fellow to form an ejaculalory duct, with 

 about half a dozen cement glands (c. gl. ). The ejaculatory 

 bursa or bell-lilie copula tory organ (6), and has at its 

 opening a small papilla acting as a penis. 



In the female the ovary is connected with the sus- 

 pensory ligament (Figs. 252 and 254, s.lg.). When 

 ripe, groups of ova — known as the " swimming ovaries " 

 (s.ovy.) — become detached and swim freely in the body- 

 cavity, wliere tliey are impregnated. The ducts are 

 very peculiar. Connected with the end of the sus- 

 pensory ligament is a muscular vJeriiie bell (6), widely 

 open anteriorly (Fig. 254, x) into the ccelome, and 

 lla^^ng towards its posterior end a small aperture, also 

 communicatmg with the ccelome (y). The bell is con- 

 nected with a narrow double passage leading to a 

 uterus (vf.), which itself opens by the genital aperture 

 at the posterior end of the body. The uterine bell 

 performs rhythmical swallowing movements, and as the 

 eggs — containing partly developed embryos — float in 

 the ccelome they are swallowed by the bell. The im- 

 mature eggs, which are globular, are passed back into 

 the ccelome through the posterior aperture (y) of tlie 

 hell ; but the mature eggs, whicli are spindle-shaped 

 and covered with a chitinous investment, make their 

 way from the bell to the uterus through the narrow 

 passages, and so to the vagina. 



The early stages of development take place in the 

 ccelome. Segmentation is regular, and a peculiar form 

 of gastrula is produced, having neither archenteron nor 

 blastoccele — in other words the ectoderm and endoderm 

 are in close contact with one another, and no central . 

 cavity is enclosed by the latter. The ectoderm layer, 

 which is devoid of cell-limits, secretes a cuticular 

 membrane investing the embryo, then a second mem- 

 brane is formed within the first, and a third within tlie 

 second ; the embryo thus comes to be enclosed in a 

 triple case, which differs from an egg-shell in being 



wlrich are connected 

 duct opens into the 



ztl 



--vg 



'iG. 254. — Female organs of 

 Hchinorhy nchus . 



b. uterine bell ; s. \g. 

 suspensory ligament ; 

 ut. uterus ; vg. vagina ; 

 .T. 7/ aperture of bell ; 

 2. apertures leading 

 from bell to uterus. 

 (After Hertwig.) 



