42 BULLETIN OF THE 



siderable influence in effecting the general acceptance of similar conclu- 

 sions as to the nature of the radiate markings of the zona. Neither the 

 evidence produced by Midler, — the possibility of pressing yolk globules 

 through the " pore-canals " of the capsule, — nor the vacuolated condi- 

 tion described by Ransom ('68, p. 455), can have any direct bearing on 

 this question. 



Leuckart ('55, p. 258) appears to have been the first to assert with 

 the utmost poSitiveness that the radial striations of the zona were due 

 to pore-canals ; and although he nowhere states the exact nature of 

 the evidence which convinced him, we are doubtless at liberty to infer 

 that it was, in part at least, the kind of evidence which he elsewhere 

 ('55, p. 106, foot-note) makes use of; namely, the now well understood 

 differences in optical effects produced by elevations and by depressions 

 of surfaces. Kblliker ('58, p. 83) soon furnished additional evidence, 

 derived partly from the study of thin sections of the zona in the trout, 

 but more especially, as it appears to me, from the fact that maceration 

 in fresh water causes the middle region of these supposed pore-canals to 

 be converted into vacuoles. Aside from the arrangement of the dot-like 

 appearances as seen from the sm'face of the zona, which has been very 

 generally recognized, and the features emphasized by Leuckart and 

 Kolliker, I am not aware that any additional evidence in proof of the 

 nature of the pore-canals has yet been produced. If, then, the facts 

 warrant the description I have given of the zona in Lepidosteus, the 

 evidence that it is a canaliculation which produces the radial striate 

 markings in the zona radiata of fishes' eggs has received an additional 

 confirmation. 



Secondly. Although Miiller (as well as more recent observers) has 

 shown that the pore-canals in the outer envelope, or capsule, in the 

 case of the perch may have a spiral course, no one has hitherto observed 

 a similar feature in the case of the canals of the true zona radiata. 

 The natural injection of these canals in Lepidosteus with a substance 

 continuous with that which constitutes the villous layer, renders it 

 comparatively easy to establish the spiral course of the canals in that 

 fish ; and this makes probable the inference, that certain irregularities 

 in the direction of these canals, shown by other observers to exist in 

 the case of other fishes, may in reality be referable to the same 

 spiral condition, which, from the minuteness of the canals, has not 

 been recognized. 



