138 



Part HI. — Sixteenth Annual Report 



Physical and Chemical Changes in the Ova op some Marine 

 Teleosteans during Maturation. 



The well-known changes during maturation of a pelagic ovum are the 

 increased transparency of the yolk contents, the lowering in specific 

 gravity, and the disappearance of the germinal vesicle. In the demersal 

 ovum the same changes occur, only the processes do not go on so far. 

 That is to say, the egg does become less opaque, of lower specific gravity, 

 and the germinal vesicle disappears. Why and how do these changes 

 take place "? The increase in volume Ims been calculated by Dr. Fulton 

 iu a variety of ova, and I need only refer to his paper for a discussion of 

 this subject from the histological standpoint. At his suggestion I 

 investigated the subject from the more purely chemical side. Such 

 questions as the following came up for solution: — Does the maturation of 

 pelagic and demersal ova take place along the same lines ? That is to 

 say, does the composition of the pelagic and demersal ova alter in the 

 same way as ripening takes place ? What is the cause of the increased 

 volume and transparency, and the diminished specific gravity of pelagic 

 ova, and is the change in the demersal eggs of the same type, only lesser 

 iu degree ? Where do the constituents of the ovum come from, and how 

 are they produced when the increase in volume takes place during 

 ripening ? 



I shall divide up the work into the following sections : — 



(1.) A description of the methods employed during the research. 



(2.) Changes in volume, specific gravity, and percentage of water 

 in different pelagic and demersal ova during maturation. 



(3.) Nature of the changes in the solids, e.g., albumins, nucleo- 

 albumins, chlorides, fat, and lecithin. 



(4.) Composition of ovarian fluids. 



(5.) The role of the phosphorus in maturation. 



A. — Methods Used for Determination of Specific Gravity. 



I. Of the ovarian fluid, from unripe and ripe roes. This gave no 

 difficulty. The method was simply weighing by means of the piknometer. 

 The piknometer was weighed empty, full of distilled water, and then full 

 of fluid to be examined, e.g., Wt. of Pik. alone = P, P. -f water = P^, 



pii p 



P. + fluid = P 1 ^ ; thus p ^ _ p = sp. gr. of fluid. 



II. Of the unripe and ripe ova. This was more difficult, and in 

 many cases the results were not wholly satisfactory. Four methods 

 were employed : — 



(1.) By means of the piknometer. This is by no means a suitable 

 method, as it is impossible in many cases to get the vessel, after 

 filling it with ova, free from air bubbles. However, in the case of 

 some unripe eggs it was carried out, but the results were never taken 

 alone, but compared with those obtained by one or more of the other 

 methods. 



(2.) By measuring the ova with the ocular micrometer, then 

 calculating the volume, presuming the eggs to be spherical from the 

 4 



formula, Trr"* ('tt = 3'1416). Then a fixed number of ova 



