142 BULLETIN OF THE 



which is only about one fifth as thick as the inner. The latter is faintly 

 stained, and distinctly striate radially ; the outer is deeply stained, and 

 striations are usually not to be seen in it, but on favorable sections, espe- 

 cially such as are very thin, the striations may frequently be made out 

 to pass continuously through the whole thickness of both layers. Upon 

 this point there is not the least doubt, so that it is certain the outer layer 

 in question is truly a part of the zona, and I have been unable to find in 

 ovarian eggs any membrane intervening between this and the granulosa 

 cells. In sections of the micropylar region, the inner portion of the zona 

 radiata exhibits vacuoles elongated in the direction of the pore-canals. 

 In this region the latter are not strictly radial, but converge towards the 

 outer end of the micropylar canal. Inside the zona there is a region to be 

 seen which bears some resemblance to a membrane with coarser (more 

 distant) striations than those of the zona. It varies in thickness on dif- 

 ferent parts of the egg, and corresponds, I believe, to the sub-zonal space 

 seen in the eggs of the first stage ; but it may represent the zonoid 

 layer of His. 



The membranes of eggs of the third or oldest stage (Fig. 37) differ 

 somewhat from the conditions just described. The vacuoles of the zona 

 radiata, found in the second stage near the micropyle only, are here 

 found over all portions of the egg ; they are always most numerous near 

 the inner surface, and are not found at all in the outer fifth of the 

 membrane. They are more or less regularly arranged in series parallel 

 with the surface of the zona. Kolliker ('58, p. 84) attributed the pres- 

 ence of such vacuoles in the pore-canals to the effect of fresh water on 

 the zona. 



The granulosa cells in the second and third stages have nearly spheri- 

 cal nuclei, which lie at their distal ends (Fig. 37, Plate III.). Below 

 the nuclei, tapering columns of granular protoplasm extend to the zona 

 radiata. These columns are separated by less deeply stained tracts of 

 substance, but the boundaries of the columns are not sharply marked. 

 The appearance is as though the columnar cells were being gradually 

 metamorphosed into an intercellular substance. This condition is evi- 

 dently an approach to that found in Perca. 



The micropyle was found in eggs of both the first and second stages. 

 In the first stage (Fig. 35, Plate III.) the zona is twice as thick around 

 the micropyle as in other regions. This thickening results in a consid- 

 erable elevation of the inner surface of the zona, the outer surface being 

 only very slightly changed. The micropyle is a wide canal, the outer 

 third of which tapers rapidly and is continuous with the inner two 



