90 BULLETIN OF THE 



must certainly hhve the credit of having especially emphasized the fact 

 that after a certain epoch there exists a contrivance which prevents 

 the further entrance of water into the intracapsular space. 



I believe a comparison of the conditions in Lepidosteus with the early 

 account by Kolliker will convince the author that the villi have no con- 

 nection whatever with the interesting conditions of the perivitelline 

 space which he has discussed. 



Ryder ('86, pp. 18, 23, 30, 35, 36, and '87) has recently noted the 

 existence of a zona radiata in several species of fishes, but without 

 having given the structure special attention. In some cases the eggs 

 when laid are covered with an adhesive material, the source of which 

 is not alluded to. In the case of Ictalurus albidus (white catfish), 

 there is an interesting condition of the egg membranes which he ('86, 

 p. 47, and '87, p. 535) describes as follows: "The egg membrane is 

 double, that is, there is a thin inner membrane representing the zona 

 radiata, external to the latter and supported on columnar processes of 

 itself which rest upon the inner membrane ; there is a second one com- 

 posed entirely of a highly elastic adhesive substance. The columns 

 supporting the outer elastic layer rest on the zona and cause the outer 

 layer to be separated very distinctly from the inner one. . . . This pe- 

 culiar double egg membrane, with a well denned space between its inner 

 and outer layers, is highly characteristic, and bears no resemblance to 

 the thick, simple zona investing the egg of ^Elurichthys, nor has any- 

 thing resembling it ever been described, as far as I am aware, in the 

 ova of any other Teleostean." Eigenmann ('90) has attempted to show 

 by comparisons that the whole of this double membrane is probably a 

 true zona radiata, and that the columns are protoplasmic substance 

 which occupied the pore-canals before the separation of the two por- 

 tions of the zona ; but it seems to me more probable, from the " highly 

 elastic adhesive " condition of the substance of the outer membrane, 

 that it corresponds to the villous layer in other fishes. There can be 

 no certainty, however, as to the real homology of the outer membrane 

 until it has been subjected to a more careful study with especial 

 reference to the time and manner of its production. 



Cunningham ('86) has recently rediscovered what Buchholz found out 

 upwards of twenty years ago about the peculiar egg membranes of 

 Osmerus. It is unfortunate that Cunningham overlooked the valuable 

 work of Buchholz, and the more surprising since he refers to Owsjanni- 

 kow's paper, — which I should suppose he must have consulted, — in 

 which Buchholz is cited. Cunningham gives figures and an account 



