of the Fishery Board for Scotland. 



135 



IV.— THE PHYSICAL AND CHEMICAL CHANGES TAKING 

 PLACE IN THE OVA OF CERTAIN MARINE TELEOS- 

 TEANS DURING MATURATION. By T. II. Milrot, M.D., 

 B.Sc, Assistant to the Professor of Physiology, University 

 OF Edinburgh. 



INTRODUCTION. 



At the beginning of last summer (1897) I was requested by the Fishery 

 Board of Scotland to continue some investigations which I had commenced 

 at the suggestion of their Scientific Superintendent, Dr. T. W. Fulton. 

 These investigations specially dealt with the alterations in specific gravity 

 which the eggs of the plaice undergo during maturation, and also the 

 changes in the water percentage in the same ova as ripening proceeds. 

 I also examined at that time one or two specimens of ovarian fluid, in 

 order to find out their composition. This research deals simply with the 

 subject from the physico-chemical side, and leaves the histological un- 

 touched, this latter part having been carefully worked at by numbers 

 of scientists. In the very unripe ova of such marine Telosteans as the 

 plaice, cod, haddock, one can easily make out the tunica granulosa cells 

 outside and within the ovum, composed of its vitelline membrane, en- 

 closing the vitellus iu which the germinal vesicle lies. In the immature 

 ovum this vesicle is very large, and centrally placed, and the protoplasm 

 around it varies from a finely to a coarsely granular state. When the 

 final stage of maturation is reached, a marked distention of the egg 

 occurs, and this increase in volume is accompanied by a clearing up of 

 the contents of the ovum, and the disappearance of the germinal vesicle. 



These changes occur both in pelagic and demersal ova, only, in the 

 latter, they are not so marked, the eggs appearing, even when mature, 

 not so clear as the corresponding ripe pelagic ones. The distinguishing 

 character of the demersal ovum, as contrasted with the pelagic one, is, of 

 course, the higher specific gravity, the ripe demersal ovum sinking while 

 the ripe pelagic one floats in sea water. I have purposely described the 

 changes in the most general way, as in studying the subject from the 

 chemical side one can only hope, at least at first, to map out roughly the 

 essential nature of the maturation process. 



Chemical Composition of the Ovum. 



Before I go on to speak of the methods which I employed during 

 the research, perhaps it would be advisable for me to run shortly over 

 some of the most important points in connection with the chemical 

 composition of the ovum, so far as it is known at the present day. In 

 the egg there are, as in all living cells, the two great constituents, 

 protoplasm and nucleus, with, in addition, that structure of secondary 

 importance — the cell wall. In the first place, I shall discuss the nature 

 of the protoplasm. 



