262 



COMPARATIVE ANATOMY 



CHAP. 



at the time of sexual maturity, or through nephridia which are 

 permanently transformed into genital tubes. 



In Sternaspis, in the female one ovary is found, and in the male one testis. The 

 genital gland in both sexes has the form of a four-lobed pouch, which lies between 

 the loops of the intestinal tube, and passes into 2 efferent ducts opening outwards, 

 between the 7th and 8th segments. The genital products do not enter the body 

 cavity, but pass from the cavity of the genital gland to the exterior through the 

 efferent ducts. The question as to whether these ducts represent modified nephridia 

 must be decided by further research. 



The Myzostomidce (Figs. 175 and 176) are hermaphrodite. Their 

 sexual apparatus does not easily admit of comparison with that 

 of the other Annulate,, but rather recalls in many points that of 



FIG. 175. Organisation of Myzostoma cirriferum, after v. Graft. To the left the parapodia 

 (p), the suckers (sri), and the male genital apparatus are represented. To the right the enteric 

 branches (da) and ovaries (o). c, Cirri ; php, pharyngeal tentacles ; ph, pharynx ; pht, pharyngeal 

 pouch ; m, stomach (mid-gut) ; ed, hind-gut ; u, uterus ; wo, female genital aperture, which enters 

 the cloaca; Mo, aperture of cloaca; pm, muscles for moving the parapodia; mo, male genital 

 aperture ; si, sperm vesicle ; vd, vas deferens ; h, testes ; p, parapodia with hooks and supporting 

 rod. 



the Platodes. It is, however, probable that this is more a case 

 of analogy than of homology. In the sexually mature animals 

 the parenchyma is filled with numerous egg cells which lie in 



