92 BULLETIN OF THE 



The membrane at the poles presents thickenings which are shown by 

 the later stages to be the beginnings of the peculiar polar filaments of 

 the egg membrane. These thickenings project into corresponding de- 

 pressions of the granulosa, the cells of which are so thinned at these 

 places as to be barely discernible. When the egg has increased slightly 

 in size (21 mm. long, 7 mm. in breadth), these thickenings affect the 

 external appearance of the follicle. They have the form of finger-shaped 

 processes covered with a single layer of granulosa cells, and project 

 into the connective-tissue wall of the follicle. The statement that in 

 the thinnest places (i. e. over the tips of the projections) the granulosa 

 is only .02 mm. thick, while its thickness at the exact pole of the egg is 

 .5 mm., is not borne out by the figure, and I therefore suppose that it is 

 a typographical error for .2 mm. In either event, however, the granu- 

 losa does not regain its normal thickness over the ends of the rapidly 

 growing filamentous projections of the membrane, and this fact may 

 have significance in determining the source of the membrane. The 

 author says that the membrane, if prepared in chromic acid, appears 

 homogeneous even when highly magnified ; but, if hardened in Perenyi's 

 fluid, striae perpendicular to the surface are to be seen with a high power. 

 The striae are not represented as rigidly straight and parallel ; they may 

 even branch, and are often moniliform. They have been traced to the 

 outer surface of the membrane, where the author believes they are con- 

 tinuous with fibrils of the epithelium. He is also convinced that the 

 membrane is homologous with the zona radiata of teleosts. I cannot 

 agree with him, however, in the statement, " When there are two zonoe 

 radiatse, as in Perca fluviatilis and Osmerus eperlanus, according to Ows- 

 jannikow, these seem to be simply parts of one membrane differentiated 

 in physical properties, but essentially similar in structure." 



Cunningham believes it more probable that the zona is produced by 

 the follicular epithelium than by the outermost layer of the yolk, and 

 in the following manner : " The deeper part of the elongated epithelium 

 cells is gradually changed into the zona radiata, the substance of the 

 cells being partly transformed into the substance of the membrane, 

 while threads of protoplasm, at more or less regular intervals, remain 

 unchanged, and thus give rise to the pores of the membrane." 



Against this view I would urge that a metamorphosis of the epithelial 

 cells, especially if prolongations into the membrane occur at intervals, 

 would be likely to result in the closest union between the membrane 

 already formed and its generatrix, whereas it is exactly along this line 

 that the artificial separation, which the author notes in all his eggs, 



