120 LOGY. [Vou. IX. 
and are obscured by neuromeres arising in the sameregion. I 
think that at least two of them (Fig. 4,34) should be classed 
with the former, but upon that point, I should prefer to 
reserve my judgment. I shall publish later a more detailed 
description of this region of the cephalic plate with figures of 
sections. 
If the view here expressed is true, we have a multiple- 
eyed condition in the embryos of these animals —a condition 
common enough in adult invertebrates, but not known to per- 
sist in vertebrated animals,—and this takes us one step 
towards the ancestral condition. 
While these structures have been forming, the medullary 
folds of the head have been growing upwards, rising more 
rapidly in the anterior part of the cephalic plate, around the 
optic vesicles, and more slowly further back. Figs. 4 and 5 
show embryos after the medullary folds have begun to grow 
upwards. In Fig. 5, the optic elevation (0f.) is seen from the 
outside, and also the two elevations (7, 2) corresponding to the 
first and second circular depressions behind the eye; the 
others are hidden from view in this figure bya flexure of the 
medullary fold, which, by the way, is a normal condition at 
this stage. 
For a brief time after the medullary folds meet in the median 
line, the external elevations are all visible, but that region of 
the head, behind the optic vesicles and in front of the ears, 
becomes the seat of great modifications, and the structures 
described give way to later formed ones. They are, therefore, 
not only embryonic structures, but they are also transitory in 
nature. It is a truism in development, that the more primitive 
characteristics appear first, and the secondary modifications 
come in later. The structures described are, then, among the 
most primitive that have been preserved in this group of fishes, 
and should be of significance in indicating the ancestral 
relations of the eye. 
It has been urged as an insurmountable objection by Beard 
and others that the eye cannot be homologized with any sense 
organ developed outside the neural plate. But the suggestion 
that the neural plate is undoubtedly very much widened and 
