XVII. On the modifications of the simple and compound eyes of insects

A lth o ug h the compound eyes of the Arthropoda have been examined and described with great care in former times by J. M u l l e r , -* L e y d ig ,! G ottsche, ̂and Cl a p a r e d e ,§ and more recently by M a x S c h u l t z e || and Dr. It. G r e n a c h e r ,^ the improved methods and instruments of the present time have enabled me to add considerably to the published descriptions of the eyes of insects. My attention was first directed to this subject by a paper from the pen of Dr. G r e n a c h e r . My observations do not accord well with the observations of this author, but I think this is chiefly from the fact that he has used the eyes of immature insects, which differ greatly from those of the mature insect, and from the difficulty there has hitherto been in preparing sections of sufficient thinness to allow the minute structure of the pigmented portion of the eye to be observed. I have been enabled to overcome this difficulty by imbedding the head of the insect in cocoa butter, in the manner first devised by Mr. S c h a f e r , and used by him in the investigation of the early conditions of the mammalian ovum; in this way I have been enabled to obtain sections of the requisite thinness. In the present communication the principal types of eye are described which I have found in the class Insecta. Reserving the distribution of these types in the class for a future communication, I shall merely indicate the Orders in which each type is found; and in so doing would especially draw attention to the fact that the number of species and genera which I have at present examined is far too small to enable me *§