MUSEUM OF COMPARATIVE ZOOLOGY. 83 



membranes, which are not easily separable either in the fresh state or after 

 treatment with osmic acid ; but on thin sections of eggs hardened in the 

 latter reagent or potassic bichromate the two are sharply marked. This 

 condition is held to indicate a gradual growth of the striate Dotter- 

 haut, " und zwar ihrer ausseren Stabchenschicht," which is the youngest 

 formation, the inner layer being the older. Both layers consist of rods 

 radially placed side by side, those of the inner layer being much finer, 

 longer, and nearer together than the outer. It is evident, I believe, 

 that the inner layer referred to must be the zona radiata, and the outer 

 the " Eikapsel " of Miiller. Fine granules, which are colored black by 

 the osmic acid and are regarded as yolk granules, are found in the fine 

 processes between the rods, as well as in the follicular epithelium itself. 

 When the ovary hardened in alcohol is stained in hematoxylin, the 

 inner surface of the follicular epithelium resembles ciliated epithelium, 

 since the rods rest like cilia on the epithelium. On sections of a very 

 young follicle (4.65 fx) the membrane, composed of rods, can be seen on 

 the inner surface of the follicular epithelium. It is still thin and not 

 easily detached, and the rods are fine and close together. When the 

 follicle has reached a diameter of 465 p, the membrane is much thicker, 

 and composed of two layers. It is then to be seen that in some places 

 the rods of the outer layer are continued into the inner layer, being 

 consequently longer. In this case the rods gradually diminish in thick- 

 ness as one passes from the follicular epithelium toward the yolk sub- 

 stance, but they are always sharply limited from the latter. Both layers, 

 the author concludes, are cuticular formations of the follicular epithelium, 

 and in no case is the inner layer to be regarded as a special membrane 

 produced by the egg itself. 



One of the best contributions recently made to this subject is that of 

 Brock ('78, pp. 547-559), who gives, besides a condensed summary of 

 previous observations, his own valuable results. Aside from the capsular 

 membrane of the perch, which he calls " Gallertkapsel," and the related 

 structures of other fishes, the author is able to recognize only one egg 

 membrane, which, to avoid prejudging its genetic relation, he calls, from 

 its most evident morphological peculiarity, the zona radiata, reserving 

 the term membrana vitellina for egg envelopes, which are the equivalent 

 of other cell membranes and therefore differentiations of the \_egg~\ proto- 

 plasm. The outer lamella of the zona described by Eeichert and by 

 Kolliker he finds with varying distinctness in different cases. Being in 

 some instances unable to discover it at all, he doubts its constancy. It 

 may often be demonstrated by the use of acetic acid when not visible 



