28 BULLETIN OF THE 



dosteus] have a double investment consisting (1) of an outer covering 

 formed of elongated, highly refractive bodies, somewhat pyriform at 

 their outer ends (Plate 21, fig. 17,/. e.), which are probably metamor- 

 phosed follicular cells, and (2) of an inner membrane, divided into two 

 zones, viz. : an outer and thicker zone, which is radially striated, and 

 constitutes the zona radiata (z. r.), and an inner and narrow homo- 

 geneous zone (z. r.')." In a foot-note the authors state, in addition, that 

 " the ripe ova in the ovary have an investment of pyriform bodies 

 similar to those of the just laid ova," but that their attempts to ascer- 

 tain the nature of these peculiar pyriform bodies proved futile on 

 account of the bad state of preservation of the material at their 

 command. 



A. Observations. 



The observations which I have made on the egg membranes of Lepi- 

 dosteus will be followed by an historico-critical account of what is 

 known about the structure of egg membranes in other fishes. 



I have examined the membranes in fresh eggs, as well as in those 

 which have been treated with various reagents, and have been able to 

 carry my investigation somewhat further than Balfour and Parker. It 

 will appear in the course of the following account to what extent my 

 results agree with theirs, and in what they differ. 



a. Zona Radiata and Villous Layer. 



Omitting for the present the modifications in the micropylar region 

 of the membranes, I will consider first the structure of the envelopes in 

 the recently laid egg which has not been subjected to the action of re- 

 agents, and subsequently will describe what is to be gained by the study 

 of sections made from eggs that have been hardened and stained. The 

 differences between the membranes of recently laid eggs and those of 

 mature ovarian eggs are so unimportant that it will not be necessary to 

 give a separate account of each. The nature of the differences, when 

 such exist, will be pointed out in the course of the description. When 

 the ripe eggs are artificially removed from the female by " stripping," 

 they have at first irregular, more or less polyhedral forms, due to mutual 

 pressure in the ovary, and the membrane investing each is in a pliable 

 condition. This state is retained for a long time, provided the eggs do 



Ryder here states. He seems to have entirely overlooked the existence of two 

 membranes, and gives such an account of his " zona " as to make me believe that 

 he has had in view what I have described as the villous layer. 



