MUSEUM OF COMPARATIVE ZOOLOGY. 75 



brane becomes thicker, and in Acerina punctate markings become visible 

 on its outer surface when it is only about 2.8 /x thick. There is never 

 any appearance which allows the supposition that the thickening is pro- 

 duced by secretions from the epithelium of the follicle. Since the punc- 

 tate appearance becomes visible only after the thickening of the original 

 membrane, it is to be concluded, says Reichert, that the punctate mem- 

 brane of the ripe egg is not the original vitelline membrane, but a 

 secondary egg-membrane, which, however, has been formed by the depo- 

 sition of thickened layers (" Verdickungschichten ") of the egg outside 

 the vitelline membrane. But what has meantime become of the vitelline 

 membrane is nut stated. 



Keichert distinguished on the majority of the eggs which he studied a 

 second membrane outside the punctate one. In Esox it was clear, homo- 

 geneous, and viscid. In cyprinoids it had the velvety appearance already 

 described by Midler, from whom the author differs in regarding this 

 membrane as not a part of the punctate one. His reasons for this con- 

 clusion are, that it is as sharply marked from the punctate membrane 

 as is the capsular membrane in the perch and may even be detached 

 after treatment with chromic or nitric acids, that the rod-layer is not so 

 firm as the punctate, and finally that the rods are much fewer than the 

 punctations of the same egg. The rods are set in a clear, homogeneous 

 layer, only their rounded ends protruding. 



Reichert was evidently influenced by his belief in the probability that 

 the capsular membrane in the perch owed its origin to the membrana 

 granulosa, and consequently he left unsettled the question of the origin 

 of this villous layer, although its intimate adhesion to the punctate 

 membrane indicated a common origin with the latter. 



Kolliker ('57, p. 197) found in 185G that the porous membrane in 

 the case of sturgeons' eggs presented conditions which favored the view 

 that it was formed by the cells of the follicle, but he discreetly abstained 

 from forming an ultimate judgment before eggs in all stages of develop- 

 ment had been studied. Such studies he found the opportunity of be- 

 ginning during a sojourn at Nice a few months later, and he continued 

 them on fresh-water fishes during the beginning of the following year • 

 the results were published in 1858. 



Kolliker's ('58, pp. 80-93) observations embraced a large number 

 of fishes, and — what is of more importance — he also studied eggs in 

 several stages of development. With Reichert, he recognized two cap- 

 sular egg membranes, which he called " Dotterhaut " (zona radiata) and 

 " Gallerthulle" (the latter in Perca), but he dissented from Reichert's 



