VI 



PHYLUM NEMATHELMINTHES 



315 



suspensory ligament. From each a vas deferent (v. r//.), furnished with several 

 vesiculce seminal ex or sacs for the storage of spermatic fluid, passes backwards 



FIG. 253. A, longitudinal section through the terminal twigs of the nephridia of Echino- 

 rhynchus gigas ; highly magnified. , nucleus. B, a terminal twig more highly magni- 

 fied. 6, the porous membrane. (From Shipley, after Kaiser.) 



and unites with its fellow to form an ejacitlatory duct, with 

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

 bursa or bell-like copulatory 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 " 

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

 cavity, where they are impregnated. The ducts are 

 very peculiar. Connected with the end of the sus- 

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

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

 having towards its posterior end a small aperture, also 

 communicating with the coelome (y). The bell is con- 

 nected with a narrow double passage leading to a 

 uterus (nt.}, 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 ccfilome they are swallowed by the bell. The im- 

 mature eggs, which are globular, are passed back into 

 the coelome through the posterior aperture (y] of the 

 bell ; but the mature eggs, which 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 

 blastocrele--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 the 

 second ; the embryo thus comes to be enclosed in a 

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



which are connected 

 duct opens into the 



-sly 



FIG. 254. Female organs of 

 Echinorhy nchus . 



b. uterine bell ; .. Iff. 

 suspensory ligament ; 

 n t. uterus ; v<i. vagina ; 

 .'. ?/. aperture of bell ; 

 z. apertures leading 

 from bell to uterus. 

 (After Hertwig.) 



