264 COMPARATIVE ANATOMY CHAP. 



on the asymmetrical ventral vessel. According to recent research it is probable that 

 in most, perhaps in all, Brachiopoda the sexes are separate. The germ glands are 

 outgrowths of the endothelium of the body cavity, and lie as branched or reticulated 

 strands, in the Tcsticardincs in pairs in the body cavity of both mantle folds, in the 

 Ecardines in the mantle folds and in the body cavity of the trunk, or in the latter 

 alone (Fig. 150, p. 226 ; Fig. 177, p. 263). 



In the Priapulidce the anal tubes, which in early stages act as excre- 

 tory organs, become later the places of formation of the genital products. 

 They are then at the same time germ glands and efferent ducts. 



In the Bryozoa there seems to be no definite rule ; separation 

 of the sexes is sometimes found, and at other times hermaphrodit- 

 ism. The ovaries and the testes arise, in the Edoproda, as cell out- 

 growths on the inside of the body wall or on the funiculus. The 

 first position is most characteristic of the ovaries, the second of the 

 testes. In the fresh-water Bryozoa, however (Fig. 139, p. 208), there 

 also arise on the funiculus the statoblasts, which are to be regarded as 

 parthenogenetic eggs. Special efferent ducts are wanting. The eggs 

 and spermatozoa fall into the body cavity. We do not yet know for 

 certain how they reach the exterior. Many observers maintain that 

 in hermaphrodite Bryozoa self -fertilisation takes place in the body 

 cavity. In many marine Edoprocta (Cliilostomata and some Cyclostomata) 

 the ripe (fertilised) eggs are taken up into special capsule-like foldings 

 of the body wall, the so-called ooeeia or ovieells, and these are 

 regarded as modified individuals which have arisen by gemmation. 

 This view does not as yet rest on sufficient foundation. The sexe& 

 seem to be separate in the Endoproda, but it may perhaps be the case 

 that the ovaries and testes do not develop at the same time. Two 

 testes lie between the stomach and body wall, and pass into 2 

 sperm ducts, which emerge into a sperm vesicle, the latter opening by 

 a pore into the vestibulum (the depression between the tentacles at 

 the bottom of which the mouth lies). The female genital apparatus 

 shows a similar arrangement : 2 ovaries, 2 oviducts, and an un- 

 paired terminal division which also opens into the vestibulum by a 

 pore. The genital apparatus of the Pterobranchia is not yet sufficiently 

 known ; under the 2 eyes of Cephalodiscus lie 2 ovaries. 



Rotatoria (Fig. 161, p. 245). Separation of the sexes here pre- 

 vails. The usually unpaired, seldom paired, female germ gland lies 

 near, generally below, the intestine, and consists of two parts a 

 germarium, which yields the egg germs, and a vitellarium, which 

 richly supplies the young cells with yolk. The germ gland, which we 

 may call the germ-vitellarium, is surrounded by a membrane which 

 passes into a fine oviduct opening into the cloaca. The last part of 

 the oviduct, where the eggs often remain for some time, may be called 

 the uterus. In the male a testis with a vas deferens and protrusible 

 penis are found, which latter lies at the posterior end of the body ; 

 through it also the contractile terminal vesicles of the nephridia open 

 outwardly. 



