64 ROBERT SCHARFP. 



following Balfour and others in adopting this name for the 

 principal membrane. As it is probably in all cases pierced by 

 radiating pores, the term " zona radiata " indicates its most 

 prominent morphological character. The name " vitelline 

 membrane " is misleading, additional membranes having been 

 described, some of which no doubt owe their origin also to the 

 vitellus. I believe one of the principal causes of the very 

 great divergence of opinion as to the number of membranes, is 

 that in some cases only intra-ovarian and in others ripe ova 

 have been examined. Balfour x has shown in his careful 

 researches on the intra-ovarian egg of Elasmobranchs, that in 

 many cases an absorption of part or the whole of the mem- 

 branes takes place. The disappearance of the "zonoid 

 layer " in the ripe ovum of the gurnard, shows that such an 

 absorption may also occur in Teleosteans. The ova of Lepi- 

 dosiren, described by Beddard, 2 afford another example of an 

 imbibition of the membrane taking place. I may mention 

 here incidentally that I am inclined to look upon his zona 

 radiata as the above-mentioned zonoid layer. 



In Trigla gurnardus the zona radiata in section does not 

 show a distinct striation, but in the fresh egg it is well visible. 

 Its thickness (figs. 8, 13, 14, 15, z.) averages about 0"008 mm. 

 It is often granular and stains darkly as a rule in carmine and 

 hsematoxylin. Internally to it is a much broader layer (figs. 

 8, 13, 14, 30), which in section appears to be the inner por- 

 tion of the zona, the stripes being apparently continued through 

 both. The width of the latter is about 0025 mm. Both layers 

 are striped, i. e. provided with minute radial pores. I was in- 

 clined at first to consider these two layers as belonging to one 

 membrane, namely, the "zona radiata/' 



However, its semi-fluid condition distinguishes it from the 

 much firmer and elastic zona radiata. Hitherto it has always 

 been looked upon as the outer portion of the yolk, and has been 

 described by Gegenbaur in the ova of birds, reptiles, and 

 Elasmobranchs as the " helle Randschicht," and by His as the 



1 Balfour, loc. cit. 

 * Beddard, loc. cit. 



