76 BULLETIN OF THE 



explanation of the striate appearance of the former, and demonstrated 

 by means of thin sections that it was due to the presence of pore-canals. 

 Kolliker also claimed that there was an outer thin, resistant layer of 

 the porous vitelline membrane in the case of all fishes, — such as 

 Leuckart alone had recognized in Perca, — and that this layer might 

 retain the striate appearance even when the rest of the membrane had 

 been made pale and apparently homogeneous by the use of reagents. 

 It is in this outer layer that the viscid and fatty-looking "Zottchen'' 

 are rooted with their slightly enlarged bases. Kolliker therefore re- 

 gards the " Zottchen " layer as belonging to the " Dotterhaut," rather 

 than as a separate layer, and compares its elements to the peculiar 

 appendages discovered by Haeckel in the ScomberesocidEe. To these 

 he adds a description of peculiar mushroom-shaped appendages of the 

 vitelline membrane in Gastei-osteus and Cottus gobio. There is, how- 

 ever, one difference between the "Zottchen" and the mushroom-shaped 

 bodies ; in caustic potash the former are greatly swollen and become 

 pale, whereas the latter are made to shrink somewhat and to become 

 darker. 



In reference to the origin of this membrane and its appendages, 

 Kolliker gives the first positive information which we have, for Eei- 

 chert's conclusions were at best only theoretical and tentative. Both 

 in the case of Gasterosteus and Cobitus barbatula he showed that the 

 villous structures made their appearance before the zona radiata. In 

 the case of the first-mentioned species, the mushroom-shaped bodies 

 were distinguishable as minute wart-like points resting on the outer 

 surface of a membrane so thin that it presented only a single contour. 

 As these wart-like structures continue to occupy the outer surface of 

 this vitelline membrane while the latter increases in thickness, it is not 

 to be doubted, he says, that the increase is due to deposits upon the 

 inner surface of the membrane. The warts continue to increase in size, 

 while the membrane becomes still thicker and shows radial markings. 



The first appearance of the villi in Cobitis is to be seen in eggs 

 0.08" [0.08'"]= 175 /x] in diameter, where they appear as deposits or 

 outgrowths on the external surface of a thin membrane (Reichert's primi- 

 tive vitelline membrane) ; at first they are low and narrow, but they 

 gradually increase in length, and also, though more slowly, in breadth. 

 It is only when the villi have attained their full length that the porous 

 layer begins to be formed by deposits on the inner surface of the thin 

 membrane, but this proceeds with such energy that the porous layer 

 soon exceeds in thickness the villous. At the same time the villi in- 



