182 WILLIAM WALLACE. 



Eigenmann, is the pi'oduct of the follicular epithelium, 

 and the tubules which it contains are filled with processes 

 of the follicular cells. Previously Brock (1878) had thus 

 described this membrane : — " The follicular cells, which are 

 at first in close contact with the young egg, are raised up 

 from the zona radiata by the developing gelatinous layer, 

 and, with the advancing growth of that layer, are drawn out 

 into long processes, which can be followed up to the zona." 

 According to Mark, 'Hho process by which the capsular 

 membrane is formed is neither simply a cell secretion nor 

 exclusively a cell metamorphosis." I have come to a similar 

 conclusion in regard to the egg membrane of Chimasra 

 (fig. 30). This figure may be compared with Brock and 

 Mark's description of the capsular membrane of the perch. 



Another example of an egg membrane formed from the 

 follicular epithelial cells is, according to Eigenmann, the 

 outermost thin homogeneous membrane, with or without 

 appendages, found in Fundulus, Pygosteus, CI u pea 

 vernalis, etc. In regard to C. vernalis, Eigenmann says, 

 ^^This outer membrane is intimately connected with the 

 granulosa cells, so that it usually retains its connection 

 with the granulosa when the latter is artificially separated 

 from the zona. In all cases slender striations extend from it 

 to the zona radiata." I have found in Zeus faber a mem- 

 brane which seems to answer very well to this description 

 (fig. 34). 



Eigenmann considers that the zonoid layer, seen by him 

 in immature eggs of Amiurus, is an artificial product, duo 

 to the contracting effects of reagents employed in preparing 

 the ova for sections. The charactei'istic appearance of the 

 zonoid layer — that of radially arranged fibrils nnderneath the 

 zona — is caused " by the partial withdrawal of the protoplasm 

 occupying the pore canals of the zona." " Such an origin of 

 the zonoid layer would," he says, " also explain its disap- 

 pearance in ripe eggs. After the egg has attained its full 

 size the connection of the yolk with the substance in tlie 

 canals would naturally be less intimate than at an earlier 



