72 BULLETIN OF THE 



fairly claimed that he had seen the pore-canals ; but even in that case 

 it remains perfectly evident that he did not understand at all the 

 structure of the zona radiata. 



When, a few months later, Remak ('54) announced the discovery of 

 radial striations traversing the whole thickness of the zona pellucida in 

 the case of the rabbit's egg, and attempted to determine the cause of 

 the appearance by a comparison with the conditions found in the egg 

 membrane of a fish (presumably Gobio fluviatilis), Miiller ('54 a , p. 256) 

 was unable to agree with him in the conclusion that the appearance was 

 probably due to "an alternation of canals and cylinders," but en- 

 deavored to show that it was " merely an optical expression of the sum- 

 mation and partial superposition of the images of the rods [Zapfen] as 

 seen when viewing the vitelline membrane in profile." The images of 

 the overlying rods which fall in one line would, in his opinion, cause 

 the striations to appear much longer than the individual rods really 

 were, and thus make the lines appear to traverse the whole thickness 

 of the membrane. 



Ransom ('56) maintained that there was present at an early stage 

 in the growth of the ovum of Gasterosteus a very thin membrane, hav- 

 ing a finely and regularly dotted structure ; but he does not appear to 

 have realized as yet that the dots were evidence of pore-canals. He also 

 discovered that in older eggs the part of the membrane immediately 

 surrounding the micropylar depression exhibited a number of cup- 

 shaped pcdiculated bodies scattered over its surface. These have since 

 been claimed by Kblliker ('58, p. 81) and subsequent authors to be the 

 localized equivalents of the " Zapfen " layer discovered by Miiller. 



In the same category must also be placed the remarkable filamentous 

 structures discovered by Haeckel ('55) on the eggs of several of the 

 Scomberesocidse. Although Haeckel described the filaments as lying 

 inside the finely punctate vitelline membrane (zona radiata) and having 

 no connection either with it or the yolk, there can be no doubt, as 

 Kolliker ('58, p. 81) first showed, that they are really outside the zona. 

 I have not yet had the opportunity of examining the eggs of any of the 

 Scomberesocidse, but conjecture that the sheath which envelops the bases 

 of their filaments may be only a part of a membrane external to the 

 true zona radiata, and comparable with that which Eigenmann ('90) 

 has found in Fundulus. 



Leuckart ('55, pp. 257-264), who in an appendix to his celebrated 

 paper on the micropyle of insects' eggs deals, at least incidentally, with 

 the structure of the egg membranes in fishes, was the first to perceive 



