MUSEUM OF COMPARATIVE ZOOLOGY. 59 
and Bourne are to be accepted, it would appear that the lateral eyes pre- 
sent; a much simpler type than the median eyes, —so far, at le&st, as 
regards the relation of the retinal layer to the hy podermis, the point upon 
which the interpretation essentially turns. 
It is of importance in the consideration of this question that in neither of 
their figures (Lankester and Bourne, Figs. 2, 3, 4) are the “ interneural ” 
cells represented as reaching to the cuticular lens. They form a layer, 
— uninterrupted except by the narrow nerve-fibre prolongations of the 
retinal cells, — the individual elements of which are wedged in between 
the posterior ends only of the cells composing the retina. Nothing in this 
relation stands in the way of these interneural cells being directly com- 
pared with the posterior layer of the retinal infolding in spiders’ eyes. 
The only serious obstacle to a direct comparison with ¢triplostichous eyes 
is the absence of a true “ vitreous.” 
The authors affirm with great positiveness the entire absence of the 
vitreous layer. There are two considerations which make it appear to me 
possible that Graber in figuring that layer may not have been so grossly 
in error as they claim. There are great differences in the thickness of the 
“vitreous ” in the aduit eyes of different Arthropods. (Compare Gren- 
acher, ’79, Figg. 28 and 31.) It is possible either that a very thin layer 
of cells may have been overlooked by Lankester and Bourne, or that, 
after secreting the substance of the cuticular léns, the “vitreous” cells 
are in the adult crowded to the margin or completely obliterated. 
If, then, it should happen from any cause whatever (e. g. the extreme 
thinness of the layer, or its prompt degeneration and disappearance after 
secreting the lens) that the ‘ vitreous body” had escaped the attention 
of these authors, as suggested by Lowne (’84, p. 416), then one might 
readily conceive that the lateral eyes of scorpions were formed on practi- 
cally the same plan as the median eyes of the scorpion and the pre- 
nuclear eyes of spiders. In that event the cells called by Lankester 
and Bourne “interneural” would doubtless represent the posterior of 
the infolded layers.* 
Although Graber (’79, Fig. 4) has given a figure of the lateral eye 
(Scorpio europzeus) which in some respects is much less satisfactory than 
* If this were the case (compare Lankester and Bourne, op. cif., ‘‘ Explanation of 
the small italics in all figures” and explanations of Figs. 7 and 8), the question 
raised by the authors — whether the ‘‘ pigmentiferous cells” (yp) within the retinal 
capsule of the central eye were equivalent to the ‘‘ interneural epithelial cells” (gq) 
of the lateral eyes, or were ‘‘ intracapsular (intrusive) connective tissue” — would 
be answered in favor of the former of the two possibilities. 
