OVARY AND OVARIAN OVA IN CERTAIN MAEINIi FISHES. 113 



been overlooked altogether. They are separate small vacuoles 

 distributed singly in the yolk. The yolk itself consists 

 throughout of rather large spherical globules, which in my 

 sections contain in their interior refringent granules. 



Pelagic Eggs containing no Oil Globules. 

 In figs. 14 and 15 are represented two stages in the deve- 

 lopment of the yolk as seen in sections prepared from the ovary 

 of a large plaice taken from the aquarium, and killed on 

 August 25th. The zone in which the yolk is already de- 

 veloped is much more sharply defined from the inner proto- 

 plasmic zone than in eggs which contain oil globules. The 

 yolk layer continues to become thicker in proportion to the 

 layer of cytoplasm internal to it, until it reaches the surface of 

 the germinal vesicle. The formation of yolk globules com- 

 mences at the periphery of the cytoplasm, and in consequence 

 of the absence of oil globules, when eggs of this kind are 

 examined in the fresh state, no dark inner zone is seen. The 

 eggs become more and more opaque, but their opacity is nearly 

 uniform, except that the centre is usually more transparent in 

 consequence of the presence of the germinal vesicle. In the 

 ovaries of plaice and other fish, whose eggs do not contain 

 oil globules, transparent ova containing scattered refringent 

 globules are never seen. In the immature fish all the ova are 

 perfectly transparent, with the exception of the occasional 

 aborted ova described in a subsequent part of this paper. In 

 the spent ovary, too, all the ova are transparent, except those 

 whose maturation has been arrested, and which are dead and 

 in process of absorption. 



Structure of the Spent Ovary. 

 A spent ovary, that is one from which the annual crop of 

 ripe eggs has just been extruded, may be recognised from 

 several symptoms, of which the most certain is the presence of 

 a few ripe eggs detached from the walls of the ovary, but still 

 remaining in the cavity. When a portion of the germinal 

 tissue of an ovary in this condition is microscopically examined 



VOL. 40, PART 1. — NEW SER. H 



