OVARY AND OVARIAN OVA IN CERTAIN MARINE! FISHES. 105 



tained, can be at once recognised, having retained their form 

 and position. 



Even in the brill the oil globules at their first appearance 

 are not entirely confined to the neighbourhood of the germinal 

 vesicle, some of them being scattered in the rest of the cyto- 

 plasm. In the gurnard as seen in fig. 1, they are irregularly 

 scattered through the cytoplasm, while in the sole the greater 

 number are situated near the surface of the ovum. For the 

 present I will confine myself to pelagic eggs with a single oil 

 globule, leaving the sole to be considered separately. 



In the turbot in ripening ovaries examined in the fresh state 

 the same contrast between inner and outer zone in the deve- 

 loping eggs is observed as in the gurnard ; I believe it occurs 

 also in the brill. The fact that the outer more transparent 

 zone consists of yolk spherules, indicates that, as might be 

 expected, the yolk is formed first in these cases, as in the 

 species of Pleuronectes, at the periphery. More minute exa- 

 mination of the process must be made by means of prepared 

 sections. 



Diff'erent modes of preparation make great differences in the 

 visibility of the vitelline elements in sections. Thus portions 

 of the ovary of a brill 17j inches long were preserved imme- 

 diately after death, at sea, on September 29th, in chromic acid 

 5 per cent. This ovary is evidently in a much more advanced 

 condition than that previously mentioned, it contains eggs 

 which have reached a much larger size than any in the latter, 

 and in which the yolk is considerably developed. Yet in the 

 younger eggs, of sizes corresponding to those in the specimen 

 previously mentioned, the oil globules are quite invisible. 

 The chromic acid appears to have the effect of closing up the 

 oil-containing vacuoles. 



From what has been stated above concerning the ovary of 

 Trigla gurnard us, it is evidently possible to study all stages 

 of the development of the yolk in this species, in sections from 

 the same ovary taken at the beginning of the spawning season. 

 The earlier stages are better preserved in material treated with 

 picro-sulphuric acid and spirit. T have sections from material 



