194 PATTEN. ' [Vol. I. 



pound eye, and the position and structure of the ommatidia, 

 to show that the ommateum develops from the inner wall of the 

 primitive optic vesicle. 



The recent observations of Carriere (20, 21), Locy (28), 

 Reichenbach (24), Claus (22), and Kingsley (23), on the 

 development of the simple and the compound Arthropod eye 

 differ widely ; and it seems, at first sight, hardly possible to recon- 

 cile them either with one another or with my interpretation of 

 the structure of the compound eye. I am convinced, however, 

 that this difficulty arises from a difference in interpretation rather 

 than in observation. The compound eye and optic ganglion 

 of Vespa develop so slowly, and the successive stages are 

 so clearly defined, that it is not difficult to follow the 

 process through all its changes. The observations described in 

 this paper, it seems to me, render it easy to harmonize the 

 conflicting interpretations of facts observed by Reichenbach 

 and Kingsley, while at the same time they furnish a con- 

 firmation of my views upon the origin and structure of the 

 compound eye. 



This paper contains observations on the compound eyes of 

 Vespa, Blatta and Phryganids, and upon the ocelli of Dytiscus, 

 Hydrophilus and Phalangiiim. Only the more important facts, 

 and those of theoretical significance, are mentioned here, since 

 a more detailed account will be published later. 



VESPA. 



In unhatched embryos whose mouth-parts have just ap- 

 peared, the ventral plate extends to the anterior extremity 

 of the &g^, over the apex of which the head-end is bent at 

 nearly right angles, so that the mouth lies at the tip of the 

 egg, while the cephalic lobes are directed posteriorly and 

 dorsally. The formation of the brain is initiated by a thickening 

 of the distal and ventral edges of the diverging lobes. A gentle 

 depression soon appears in the middle of the lobes, while at 

 the same time their distal and ventral edges break away 

 from the ectoderm, which then begins to grow over them 

 (Figs. I and 2, j). Just below the free edge of the ectoderm, 

 the cells of the cephalic lobes are contracted at their outer 



