264 A MONOGRAPH OF THE AUSTRALIAN APHRODITEA, 



But, however this may be, it is not of very much consequence to 

 the present question, namely, the true position and relations of 

 the segmental organs. 



As regards the position of the sexual follicles : in Thormora 

 and Pohj?i6e I have found the ova to be developed in the bases 

 of the parapodia around the intestinal caeca, and the muscular 

 bands passing from the latter to the body-wall, or along the 

 middle ventral line around the ventral vessel. A representation 

 of the developing ova is given in plate vi., fig. 3. They arise 

 from nuclei formed in a membrane covering those parts, which 

 membrane seems to be merely a modified portion of the peritoneum, 

 and probably these '^ ovaries " are only temporar)^ structures, 

 and not to be detected save during the season of sexual activity . 

 The matured ova when set free float freely in the fluid of the 

 perivisceral cavity and afterwards collect into clumps, two in each 

 segment, situated a little internally to the bases of the parapodia. 

 Such as fail to be discharged subsequently undergo a process of 

 degeneration, lose their full, rounded contour, become crenated 

 or mulberry-like, and probably finally become broken up and 

 absorbed. 



The spermatozoa are formed in follicles which are situated, like 

 the ovaries, either along the middle ventral line of the body (pi. 

 vi., fig. 3) or around the intestinal coeca. Each follicle in 

 Polynoe prceclara is a lobed mass situated in the interval between 

 two segments ; along the axis of the follicles runs the ventral 

 pseudohaemal vessel ; in Thormora argiis they are vermiform 

 bodies situated between the branches of the gastric ca3ca in the 

 lateral portions of the perivisceral cavity. The spermatozoa 

 themselves are rod-like with a slightly thickened head in Antlnoe\ 

 oval in Thormora argiis. Further observations are necessary for 

 a thorough understanding of the mode of development of these 

 and of the ova. 



