274 



T. IWAKAWA. 



epithelium. In all ova under 1 mm. in diameter, the cortical 

 layer of protoplasm follows closely the boundary of the cells 

 of the granulosa, as seen in fig. 21. 



In ova measuring about 1 mm. may be seen a thin super- 

 ficial portion of the cortical layer, quite transparent and 

 free from granules (fig. 24). The outer contour of this thin 

 layer is sharply defined, but there is as yet no line of division 

 between it and the cortical zone. This surface stratum of 

 the cortical layer, which is about "001 mm. thick, is the 

 vitelline membrane in process of formation. In an ovum 

 of 1*5 mm. (fig. 25, v. m.) it has taken the form of a double- 

 contoured membrane, which appears to be perfectly homo- 

 geneous. In this section, which was treated with chromic 

 acid (i per cent.) and Beal's carmine, the membrane was ^ 

 stained more deeply red than the underlying protoplasm 

 There is no doubt in my mind that the membrane seen in 

 fig. 25 is identical with the clear surface stratum in fig. 24 ; 

 and as in the latter figure it is continuous with the proto- 

 plasm, I regard it as a modified part of the protoplasm, and 

 hold that the vitelline membrane is produced by the egg 

 itself, and not by the granulosa. 



The Germinal Vesicle. 



My observations on the germinal vescicle, especially on 

 its earlier stages of growth, are quite incomplete. In ova 

 measuring about '26 mm., examined in a fresh condition, the 

 germinal vesicle appears perfectly clear, is spherical, and 

 has a somewhat excentric position (fig. 20). 



Numerous germinal dots f'OOS mm.) lie at the very surface 

 of the nucleoplasm (Van Beneden), apparently in contact 

 with the inner surface of the very thin delicate membrane 

 of the vesicle. In ova hardened in picro-sulphuric acid and 

 stained with haematoxylin the nucleoplasm has a reticulate 

 appearance (figs. 19 and 27). Cases like that seen in fig. 19 

 occur not infrequently, in which the nucleoplasm has con- 

 tracted more than the membrane, in which case the germinal 

 dots remain adhering to the membrane. In other cases the 

 membrane follows the contracting nucleoplasm, as seen in 

 fig. 27. In fig. 22 is seen a germinal vesicle, of about the 

 same size as that seen in fig. 27. The ovum from which 

 fig. 27 was taken corresponded also very nearly in size with 

 the one given in fig. 22. In fig. 22 the germinal vesicle 

 appears to lie in a large cavity, or rather to be suspended 

 from one side of the cavity. This cavity, if it existed in the 

 living egg, was undoubtedly filled with a watery fluid, upon 

 which the staining fluid had no visible effect. In fig. 27 the 



