GO 



largest ova in the ovary at this stage are still verj' young, and each consists of a 

 protoplasmic mass containing a nucleus. The nucleus is a spherical vesicle bounded 

 by a membrane and containing protoplasmic strands and a number of nucleoli 

 which are all situated at the periphery of the nucleus. In a stained preparation the 

 nucleoli and the protoplasm of the ovum surrounding the nucleus are deeply stained, 

 but the rest of the nucleus, consisting chiefly of liquid contents, is scarcely stained at 

 all. Thus in each ovum the nucleus is seen as a clear central space containing several 

 deeply stained globules arranged within its external border. There is little doubt 

 that the fibrous connective tissue in the living state is more compact than I have 

 represented it to be. The ova contract in the process of preparation and leave open 

 spaces between them across which fibres are seen passing. But nevertheless it is 

 certain that the fibrous tissue is reticular, and that it is traversed bj* spaces containing 

 lympli. 



When a portion of an ovigerous lamella from a young ovary is examined with a 

 high power it presents the appearance shown in PI. XIII, 2. The preparation from 

 which this figure is taken was made from the ovary of a sole 10^ inches long, killed 

 in January. This also was an ovary which had never produced ripe ova, an im- 

 mature ovary. It will be seen that the cells of the germinal epithelium are extremely 

 minute and their outlines undefined. The ova are evidently produced by the 

 enlargement of single cells of this epithelium, and as they increase in size they pass 

 downwards into the fibrous "stroma." Even round the largest ova in an ovary at 

 this stage no envelope can be detected except a fibrous membrane belonging to the 

 "stroma" of the ovary. The protoplasm of the ovum, although it has grown in 

 quantity, still exhibits no differentiation. The largest ovum represented in Fig. 2 is 

 •12 mm. in diameter. 



But ova which are approaching maturity show a much more complicated structure. 

 Fig. 3 is drawn from a section prepared from an ovary in the spawning condition ; 

 in fact the ovary was almost spent, but a few immature ova remained in it, and a 

 section of one of these is represented in the figure. This ovum is seen to be enclosed 

 by a thick envelope, exhibiting in section close set radiating lines. This envelope is 

 not stained in the preparation. The radiating lines are really exceedingly fine tubules 

 passing through the substance of the envelope and through these the protoplasm of the 

 ovum communicates with the nutritive fluids outside. This envelope is the innnature 

 stage of the membrane surrounding the ripe ovum when it is shed, but at this stage it 

 is much thicker in proportion to the size of the ovum than in the state of maturity. 

 This envelope may be called the vitelline membrane ; in the eggs of some fishes it is 

 differentiated into two layers, but in the sole I can find no distinction except that the 

 exterior surface of the membrane forms a kind of thin cuticle. The ovum within the 

 membrane presents an appearance very different from that of tlie j-ounger ovum 

 previously described. Instead of a mass of granular protoplasm there are here a great 

 number of spherical vesicles crowded together. These vesicles contain a number of 



