148 



r. I REDA. 



question (a in A, C, E) is in a state in which the smaller and little stained 

 constituent is already completely inclosed within the other. The former, 

 after the inclosure, swells and produces within it a few vacuoles. The 

 second nucleolus (ri), in an early part of the ovogenesis, is of a homo- 

 geneous appearance, staining deeply hy nuclear stains (fig. 4, A & B, ri). 

 However, after growing in size to a certain degree, it likewise becomes 

 vacaolized (fig. 4, D & E, »'). 



Very remarkable is the occurrence within nucleus of a small lightly 

 stained body shaped like a comma ; it is found attached by its narrower 

 end to the inner surface of nuclear membrane. It seems to be formed 

 after the oocyte has advanced considerably in growth (see fig. 4, D & E, 

 x). I know nothing to say about its nature or significance. 



After the oocyte has grown to full size (0.2—0.3 mm. in diameter) and 

 shortly before the ovulation by dehiscence of the follicular membrane, 

 the nucleus begins to show changes preparatory to the formation of the 

 first polar globule. The nuclear membrane is slackened, the linin net- 

 work becomes indistinct and the nucleoli no longer exist as such ; at the 

 same time a number of chromatic granules make their appearance in the 

 nucleus. 



The oocyte after liberation from the ovary is spherical; it is supplied 

 with a very thin vitelline membrane. Of the cytological changes which 

 now take place in connection with the production of polar globules, the 

 detail was given in my paper on the development of Actinotrocha (Jour. 

 Sci. Col., Vol. XIII, 1900). Suffice it to say here that so long as the 

 oocyte remains in the coelomic cavity, the nuclear division figure is in 

 the mesophase or in the metaphase. The chromosomes belonging to it 

 consist, in P. ijimai, of six pieces ; in P. australis there are twelve of 

 them. The expulsion of the first polir globule takes place after the oocyte 

 is expelled to the exterior through the nephridial funnels, at a time when 

 it is met by the free-swimming spermatozoa. This is soon followed, 

 without rest, by the formation of the second polir globule, — the well 

 known reduction division, by which the chromosomes are reduced to half 

 the normal number. Thus, in P. ijimai the fully mature ovum is in 



