84 BULLETIN OF THE 



in the fresh condition. In the perch it has a striate appearance, and 

 is much more coarsely marked than the true zona, 1 but in Serranus 

 hepatus it is homogeneous. 



The elongated club-shaped villi resting upon the outer surface of the 

 zona were found in many cyprinoids, and also in Osmerus. They are 

 not, as asserted by Eimer, expressed droplets of yolk substance ; they 

 are secondary appendages of the zona, which " have nothing whatever 

 to do with either follicular epithelium or yolk." Brock finds the zonoid 

 layer of His well developed in Alburnus lucidus, Salmo fario, and Perca 

 fiuviatilis. He is inclined to regard it as a general structural condition, 

 often overlooked because distinctly shown only at certain periods in the 

 development of the egg. It is often divisible into two layers, of which 

 the inner remains homogeneous. When the zona radiata is removed 

 from the yolk, the " zonoid " remains attached to the latter, to which it 

 must therefore belong. Its striations are intermediate in fineness be- 

 tween those of the villous layer and those of the zona. Notwithstanding 

 certain objections, Brock regards the follicular epithelium as the princi- 

 pal, if not the exclusive, source of nutrition and growth for the yolk, 

 which are accomplished by means of cell processes sent by the granulosa 

 through the zona into the yolk. The evidence, aside from that which 

 Waldeyer produced fur other groups, is to be found, says Brock, in the 

 fixct that, when the granulosa is separated from the zona by a secondary 

 membrane (Perca, Serranus), it sends processes through the latter which 

 are traceable up to the zona. 



According to the opinion which I have formed, however, in regard to 

 these so called processes, they are not outgrowths from the granulosa 

 cells ; on the contrary, the cells, retaining their original contact with 

 the zona, are by the accumulation of the capsular secretion greatly 

 attenuated. 



In regard to the order in which the different membranes make their 

 appearance, Brock comes to views diametrically opposite to those ex- 

 pressed by Kblliker. Leaving out of consideration the capsular mem- 

 brane, which, as Brock rightly states, is late in being formed, and the 

 outer lamella of the zona, concerning the origin of which he could dis- 



1 It is not possible to say with certainty from his figure (Fig. 7, /) whether 

 Brock regarded the striations of the outer lamella as less numerous than those of 

 the rest of the zona. They are represented as broader than the latter, and as 

 thickest at their peripheral ends, which agrees with Eigenmann's observations ; 

 but they certainly are not represented as continuous with the striations of the inner 

 portion, and in this I believe that Brock is in error. 



