MUSEUM OF COMPARATIVE ZOOLOGY. 63 
own figures (J. c., Taf. XX, Figg. 2-4) seem to me favorable to the presence 
of a cuticular partition between the two cell-layers under consideration. _ 
If there are some features of the eye in Chilopoda which seem to favor 
a method of formation similar to that traced in spiders, there are almost 
none in the case of the Chilognatha, provided the figures by Graber are 
to be superseded by the account given by Grenacher. Neither Graber 
nor Grenacher has figured anything that could be compared to the pos- 
terior layer of a retinal involution; and Grenacher denies, in addition, 
the existence of a “vitreous.” In brief, according to the latter author, 
the whole eye is composed of a single continuous layer of cells formed 
into a cup-like depression ; all, except the cells at the margin of the cup, 
are bacilli-producing elements. Whether all the cells of the depressed 
region, or only the marginal ones, are engaged in the production of the 
lens, the author does not suggest. Apparently, the only chance of there 
having been a distinct “‘ vitreous ” in this case, would rest upon the pos- 
sibility that these marginal cells at first meet in front of the retina, and 
afterwards suffer a complete centrifugal displacement ; but of this there 
is as yet no direct evidence. 
The apparent improbability of an involution with inversion in the case 
of the Chilognatha is not without weight in considering the nature of the 
eyes in Chilopoda, since the arrangement of the retinal cells is so strik- 
ingly similar in the two groups as to render a. fundamental difference 
between them highly improbable. Further, the almost strictly sym- 
metrical (radial) arrangement of the parts in all Myriapoda stands in 
contrast to a very common obliquity in the eyes of spiders. So, not- 
withstanding the several arguments which I have presented in the case 
of the Scolopendride favorable to an involution with inversion, I am not 
entirely certain that such has really taken place. While the evidence 
strongly inclines me to a belief in a process of inversion for Chilopoda, I 
agree with Grenacher that nothing short of a study of the development 
of the eyes is likely to afford an absolutely satisfactory answer. 
I am not able to read Sograff’s paper (80), published in Russian ; but 
in his preliminary paper (’79) he does not seem to have recognized any 
difference between the structure of the eyes of coleopterous larve and of 
spiders.* 
In the case of Hexapoda the simple eyes of the larve and the ocelli 
of the adult are sufficiently different to require separate consider- 
* “The eyes of the Lithobide and Scolopendride are exactly like the eyes of the 
larve of Acilius and other Coleoptera, as well as those of the spiders” (Sograff, ’79, 
p. 17). 
