554 



LOCV. 



[Vol. XI. 



they are in Squalus. As far as I am able to discern, there is 

 no very distinct differentiation of the optic vesicles, in the 

 early stages of this form ; nevertheless, they are present at the 

 stage designated C, by the Zieglers, and perhaps a little earlier. 

 In studying the actual specimens, I had occasion to note that 



if % 



■'''<i>i;i.V.-.»-''''' 



•Si'Oi'iVjft" 



f%ii 



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Cut io. — Twelve transverse sections of the embryo shown in PI. XXVI, Fig. 23. x about 30 

 diameters. The numbers below the sections refer to their positions in the series. In Section 

 14 the optic vesicles show below and the depressions for the mid-brain vesicles above. 



the Zieglers' models are admirable representations of the em- 

 bryos of the form they are intended to represent. The optic 

 vesicles are much fainter than they are in Squalus, but never- 

 theless are similar to them. I have studied them in Torpedo 

 both in surface views and in sections. One noteworthy fact is 

 that they have been sectioned and actually figured by Ziegler in 

 his PI. IV, Fig. 191. It will be noted in this figure, that the 

 brain-walls bulge outwards on either side and these depressions 



