146 



Part III, — Sixteenth Annual Report 



If we take as a typical example of the demersal ovum that of the , 

 herring, we note that the increase in weight of the fresh ovum during 

 ripening does not proceed nearly so far as in such a typically pelagic 

 ovum as that of the plaice. 



But the total solids in the immature and mature herring ova are very 

 similar in amount, the latter, however, always containing a larger quantity 

 of solids than the former. 



That is to say, in the herring ovum, as in the plaice, the most marked 

 change during maturation is an entrance of water from without, and if 

 there is (as we shall see afterwards there does happen to be) a diffusion 

 from without inwards of some solids during maturation, that is partly 

 balanced by the passage from within outwards of solids present in the 

 immature ova. 



The immature eggs of Lojyhius are difficult to obtain free from adherent 

 gelatinous matter, hence it was only after repeated determination that I 

 was able to get the one given in the Table. However, the weights of the 

 immature vary as maturation goes on, and the important point after all to 

 settle is not the absolute weight of the ova at different stages of ripening, 

 but the relationships between the water and the solids in ova of different 

 weights at different stages of maturation. 



It may seem at first sight that the weights that I am dealing with are 

 so extremely small that it is impossible to avoid fallacies in drawing 

 conclusions from them, but they are the average weights derived from 

 large numbers of ova (200 to 400), so that the error must be a compara- 

 tively slight one. 



Now, although we have seen that the increase in volume in both 

 pelagic and demersal ova is due to the passage of water from within 

 outwards, we cannot draw from that the conclusion that that is the only, 

 or indeed the principal, change in maturation. 



Changes in the Constituents of the Ova during Maturation. 



As I said at the beginning of this paper, it is necessary to know tlie 

 amounts of albumin and diffusible salts in the mature and immature ova 

 in order to arrive at any definite conclusion as to the nature of 

 maturation. 



One has to be very careful in drawing conclusions from a number of 

 analyses of different varieties of ova, as in many cases it is difficult, if not 

 impossible, to get very immature ova isolated from the surrounding tissue, 

 and yet it is the very immature ova which one wishes to examine, or, at 

 least, not those which are approaching maturation. The pelagic ova 

 which I have examined especially carefully are those of the plaice and 

 whiting. The unripe and ripe eggs of the former are easily isolated and 

 analysed. 



I have at the beginning of the paper spoken very shortly of the 

 methods of analyses, but it may be better for me to give the method 

 which I emjiloyed for the estimation of the albumin in the different eggs. 



In one specimen containing a known number of eggs the water was 

 estimated, while in another a fixed weight of ova was taken (correspond- 

 ing to a known number of ova). This latter was incinerated with sulphuric 

 acid, cupric sulphate, and potassium sulphate, until all the nitrogen present 

 was fixed as ammonium sulphate. The solution was then made alkaline, 

 and the ammonia so set free distilled over into a fixed quantity of oxalic 

 acid of known strength. From the loss in acidity of the oxalic acid the 

 ammonia was calculated, and, knowing the amount of ammonia, that of 



f 



