OVARIES IN TELEOSTEAN AND ELASMOBRANCH FISHES. 177 



nucleus is conspicuous by its absence in the plaice and dab 

 in the mature eggs^ of which no oil sphei'es are present, it 

 seems reasonable to conclude that thei*e is some functional 

 relation between this peculiar substance and the oil. What 

 is the precise chemical relation between the two it is 

 impossible, at the present stage, to say. In general, fat is a 

 product of the decomposition of proteid substance, as 

 exemplified in the phenomena of fatty degeneration. A 

 special case of fatty degeneration of protoplasm will be 

 mentioned below when dealing with the absorption of ova in 

 fishes. 



That the activity of the germinal vesicle is associated with 

 the production of oil in the cytoplasm seems to be indicated 

 by the fact that it also is a centre of formation of oil droplets. 

 The oil drops peripherally situated on the site of the " yolk 

 nucleus" are, however, the first to appear (fig. 37). It is 

 certain, on the other hand, that the nucleoli are not trans- 

 formed either into oil globules or yolk spherules, as Calder- 

 wood (1891) and Scharff (1887) supposed. In all probability 

 the membrane of the germinal vesicle is, as Carnoy and 

 Lebrun have stated, imperforate, so that no transmission of 

 solid material but only osmosis can take place through it. 



I have not been able to follow with certainty the " ceutro- 

 sphere" in oocytes younger than the stage represented in 

 fig. 7. I observed, however, under moderately high powers 

 (Zeiss D, ocular 4) the karyokinetic division of oogonia in 

 Zoarces. The preparations were fixed in Bles's fluid and 

 stained in bulk with ha^malum. I have not been able to 

 follow the details of the process owing to the extremely small 

 size of the oogonia (tigs. 14, 15). 



In Lumbricus, according to Calkins (1895), the yolk 

 nucleus first appears as an irregular deeply-staining body, 

 whicix is closely applied to one end of the germinal vesicle, 

 its substance being connected with the interior of the latter. 

 It ultimately breaks up into small bodies scattered in the 

 cytoplasm. 



Katharine Foote (1896) states that in Allolobophora 



VOL. 47, PAET 2. NEW SEKIES. M 



