TUBIFEX. 373 



worms, and that these vessels give off important branches 

 which are directed backwards over the reproductive 

 organs. There are, however, no special branches from 

 these vessels to the ovaries. In one case I found quite 

 a different state of affairs on teasing out the ovary from 

 the living worm (PI. V, fig. 25). Only a portion of the 

 ovary was obtained on this occasion, but the oocytes 

 present were situated on all sides of a central " stem " or 

 rod in which a blood vessel was lying — this could easily 

 be identified by the red colour of the blood which was still 

 present in it (PI. V, fig. 25, st.). The oocytes were 

 arranged quite irregularly on the stem. Large and small 

 ones lay side by side, sometimes grouped together into 

 clusters, sometimes occurring singly. Each oocyte was 

 attached to a short branch of the main stem terminating 

 in a tiny swollen head, the oocyte itself being spherical in 

 outline, or nearly so. Opposite to each stalk a short 

 branch was given off from the blood vessel — this branch 

 entered the stalk and terminated in the swollen head 

 already mentioned. It was not possible, of course, to 

 decide what was the connection of this " ovarian vessel " 

 with the rest of the circulatory system, as the ovary was 

 completely isolated. Although I examined many more 

 ovaries I never saw this interesting condition again. 



As the oocytes contain no yolk-granules as long as 

 they remain part of the ovary, they are then most suitable 

 for purposes of examination, as the yolk-granules tend to 

 obscure the other structures in the egg (PL V, fig. 27). 

 The structure of such an oocyte of Rhynchelmis has been 

 described in detail by Vejdovsky (1884), but the descrip- 

 tion does not entirely agree with the conditions obtaining 

 in an oocyte of Tubifex, at the same age. 



The oocyte is spherical in outline] and surrounded 

 by a delicate investing membrane. The cytoplasm forms 



