VI 



PHYLUM NEMATHELMINTHES 



309 



FIG. 257. A, longitudinal section through the 

 terminal twigs of the nephridia of Echino- 

 rhynchus gigas ; highly magnified, a, 

 nucleus. B, a terminal twig more highly mag- 

 nified, b, the porous membrane. (From Shipley, 

 after Kaiser.) 



ciliary flames ; at the end of each lobe are a number of fine perforations 

 placing the contained canal in communication with the body-cavity. The 



stalk of each nephridium con- 

 tains a single main canal ; these 

 unite to form a wide median 

 dorsal 

 behind 



channel which opens 

 in the female into the 

 unpaired portion of the oviduct 

 and in the male into the ejacu 

 latory duct. 



The greater part of the body- 

 cavity is occupied by the repro- 

 ductive organs. The sexes are 

 separate, and the female is 

 larger than the male. In both 

 sexes the gonads and their ducts 

 are connected with a great sus- 

 pensory ligament (s.lg.), which 

 extends backwards from the end 

 of the proboscis-sheath. 



In the male there are two 

 ovoidal testes (Fig. 255, ts.) con- 

 nected with the suspensory ligament. From each aj vas deferens (v. df.), 



furnished with several vedtculce seminales or sacs for" 



the storage of spermatic fluid, passes backwards and 



unites with its fellow to form an ejaculatory duct, with 



which are connected about half a dozen cement glands 



(c. gl.). The ejaculatory duct opens into the bursa or 



iDell-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 



suspensory ligament (Figs. 256 and 258, s.lg.). When 



ripe, groups of ova known as the " swimming 



ovaries " (s. 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 suspensory ligament is a muscular uterine bell (b.), 



widely open anteriorly (Fig. 258, x.) into the ccelome, 



and having towards its posterior end a small aperture 



or a pair of small apertures (y), also communicating 



with the ccelome. The bell is connected with a narrow 



double passage leading to a uterus (ut.), 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 coelome they 



are swallowed by the bell. The immature eggs, which 



are globular, are passed back into the ccelome 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 



blastoccele in other words the ectoderm and endo- 



derm are in close contact with one another, and no 



FIG. 258. Female organs 

 of Echinorhynchus. 

 b. uterine bell ; s. Iff. 

 suspensory ligamen t ; 

 lit. uterus ; vg. vagina ; 

 x. y. apertures of bell ; 

 z. apertures leading 

 from bell to uterus. 

 (After Hertwig.) 



