MUSEUM OF COMPARATIVE ZOOLOGY. 63 



own figures [l. 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 to be superseded by the account given by Grenadier. 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 Scolopendridse favorable to an involution with inversion, I am not 

 entirely certain that such has reall.y 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 larvae and of 

 spiders.* 



In the case of Hexapoda the simple eyes of the larvfe and the ocelli 

 of the adult are sufficiently different to require separate consider- 



* "The eyes of the Lithobidae and Scolopendridfe are exactly like the eyes of the 

 larvfe of Acilius and other Coleoptera, as well as those of the spiders " (Sograff, '79, 

 p. 17). 



