.132 J. T. CUNNINGHAM. 



ot Pieuroriectidse. 1 have been able after some trouble to 

 couviuce mvself that it exists, aud has similar relations in this 

 species, but have only been able to detect it occasionally in 

 tlie larger of the yolkless ova, which were lightly stained. 

 My material was fixed with picro-sulphuric acid, and with 

 chromic acid alone; the latter is not very efiFective for the 

 demonstration of the body in Pleuronectid ovaries, but the 

 former brings it out very clearly in them in certain conditions 

 of the ovary. It would perhaps be more easily seen in the 

 ova of the gurnard after the use of a fixing mixtnre containing 

 acetic acid. 



In Syngnathus I have not seen any trace of the vitelline 

 body or bodies after the appearance of the yolk. As described 

 above, the yolk globules in this form appear uniformly through- 

 out the cytoplasm from the first, not as a peripheral zone 

 increasing in tliickjiess, and I have been unable to discover 

 the remains of the vitelline bodies among them. The largest 

 ovum in which I have seen it was "25 mm. in diameter, and in 

 this the formation of the yolk was just commencing. 



According to Boveri, both the centrosomes of the first division 

 spindle in the fertilised egg arise from the spermatozoon, — 

 that is to say, the spermatozoon becomes in the egg a male 

 pronucleus and a centrosome, and the latter divides to form 

 the two centrosomes of the first segmentation spindle. The 

 ripe egg on this view possesses no controsome, and for this 

 reason is incapable of self-division. 



Balbiani, the original discoverer of the vitelline nucleus, in 

 1893 identified this body as the centrosome of the ovum. He 

 concludes that it arises from the nucleus as a little bud at the 

 moment when the ovum quits the germinal epithelium. He 

 points out that the vitelline nucleus condenses around it a 

 portion of the cytoplasm more dense than the rest ; and this 

 surrounding layer he compares to the archoplasm or attractive 

 sphere around the centrosome. The vitelline nucleus may be 

 double, and the centrosome is also often seen to be double in 

 resting cells. The increase in size of the vitelline nucleus is 

 interpreted as hypertrophic degeneration. Balbiani considers 



