200 BULLETIN OF THE 
The horizontal sections shown in Figs. 22-27 (Pl. IV.) are arranged 
to represent the characteristic features of the ocular area of the deft side 
of the head, as one would observe it in passing from a dorsal to a more 
ventral position. Calling that of Fig. 22 the first section, they are the 
Ist, 3d, 6th, 13th, 16th, and 21st sections in a series from a single 
animal. Fig. 22 represents the hypodermis directly above the eyes and 
at the edge of the ocular area. The extent of this area is indicated by 
the thickened region. Two sections below this (Fig. 23) the ocular area 
is more extended, and shows a single simple depression (No. 1). It will 
be observed that the band of nuclei indicates a more marked depression 
even than the outline of the hypodermis itself. This simple depression 
in the hypodermis indicates the position of a lateral eye. The cells 
which compose the wall of the cup are wedge-shaped ; their nuclei are 
below the middle of the cells, and those cells which occupy the central 
portion of the depression are so attenuated at their free ends as scarcely 
to reach the surface. 'The basement membrane (mb.) closely invests the 
deep face of this structure, as it does any ordinary hypodermal thicken- 
ing. The sixth section, Fig. 24, exhibits a region in which the ocular 
area is greatly thickened, but it shows no depressions, and the nuclei 
extend very near to the surface. Fig. 25, seven sections deeper than 
Fig. 24, presents four cup-shaped depressions (Nos. 2, 3, 4,5), each essen- 
tially like the depression previously described. The two central depres- 
sions (Nos. 3, 4) are the largest ; next in size 1s the anterior one (No. 2), 
and smallest of all is the posterior one (No. 5). As in the case of depres- 
sion No. 1 (Fig. 23) the band of nuclei in the region of each depression 
forms a much deeper cup than the outer surface of the hypodermis. The 
basement membrane (mb.), as in Fig. 23, invests only the deep surface of 
each hypodermal cup. From this plane ventrally the hypodermis gradu- 
ally becomes thinner, and at the extreme edge of the dorsal shield the 
indifferent hypodermis is reached. (Compare Figs. 18, 20.) 
The five depressions just described are early stages in the development 
of the lateral eyes. In the adult Centrurus only four eyes are present. 
Of the five depressions seen in the embryo the most posterior (No. 5) 
of the ventral four disappears, and three remaining form the “ princi- 
pal” lateral eyes. The fourth or “accessory” eye arises from the dorsal 
depression (No. 1), which, even in the embryo, occupies a position above 
the space between the second and third depressions (Nos. 3 and 4) of 
the lower row. The presence in the embryo of a rudimentary fifth eye 
is interesting, in view of the fact that there are five eyes in the adult of 
Androctonus, as has been shown by Lankester and Bourne. It is proba- 
