82 BULLETIN OF THE 



tainly a structure which does not belong to the primordial egg, but is 

 deposited upon it from without." 



Like Waldeyer, Eimer (72% pp. 417-428, Taf. XVIII. Figs. 9-13) 

 regards the zona as a cuticular product, but, unlike him, he maintains that 

 it is produced (precisely as in reptiles) by the egg, not by the granulosa. 

 But the homology between the egg membranes in these two groups goes, 

 in his opinion, still further. The delicate membrane described by Au- 

 bert and others as external to the zona in Esox and other fishes is to 

 be regarded as a chorion, — which in reptiles is produced by the fol- 

 licular epithelium. The trumpet-shaped structures of the outer mem- 

 brane (Eikapsel) in the perch are formed from granulosa cells. They 

 are the homologues of the trumpet-like structures which the author 

 described for Coluber and placed in the category of "beaker cells." 

 The villi which repose on the outer surface of the zona are, as held 

 by Reichert, to be regarded as belonging to the second membrane, and 

 not in- accordance with Kblliker's views as the outer layer of the zona 

 itself. In Eimer's opinion they are simply yolk substance which has 

 emerged from the egg through the pores of the zona. Eimer even main- 

 tains that he has observed the protrusion and subsequent disappearance 

 of such villi. 



I have already (p. 54) given my reasons for dissenting from the use 

 which His ('73, pp. 1-3) makes of the word "Eikapsel" to signify the 

 zona radiata. According to His, the "capsule" in Salmo salar is from 33 

 to 35 fj. in thickness, the pore-canals are straight, only 1.5 to 2 /x apart, 

 and not funnel-shaped at either end. In Esox it is 16 to 17 /u. thick, 

 and has fine parallel (concentric) as well as radial markings (p. 13). 



His ('73, pp. 17, 35, 36, et passim) also discovered that in numerous 

 cases the young eggs possessed a peripheral layer of clear substance 

 which exhibited fine radial markings after treatment with certain acids. 

 This did not appear to be constantly present, nor necessarily of uniform 

 thickness. He called it the zonoid layer, and thought there was proba- 

 bly a physiological connection between it and the porous egg capsule, 

 but what the nature of that connection was, remained to be ascertained. 

 Nothing in either figures or text allows one to draw conclusions as 

 to the relative fineness of the striations in the zonoid layer and the 

 " capsule." 



In 1878 appeared three papers which dealt with the structure and 

 development of the egg membranes of bony fishes. 



A pupil of Waldeyer, Kolbssnikow (78, pp. 402, 403, 407-409), 

 states that in both Perca and Gobio the " Dotterhaut " consists of two 



