ON THK KYES OF ARTHROPODS, 181 



Ero, C. L. Koch. = Tlieridion, BL, ad par/em. 

 Ero (horacica, Wid. = Tlit'vidion v.trieqntuiti^ Bl. Near 

 Aberdeen (J. W. H. T.). 



(To lie coutiniied.) 



AN ABSTRACT OF A PAPER BY 

 Dr. H. GRENACHER ON THE EYES OF ARTHROPODS. 



By B. Thompson Lowne, F.R.C.S., 



Ophthalmic Surgeon to the Great Northern Hospital ; Lecturer on Anatomy 

 and Physiology in the Royal College of Surgeons ; Lecturer on Anatomy 

 and Physiology at the Middlesex Hospital Medical School ; lic. 



Dr. Grenacher has published a very important and 

 interesting remime of his researches on the structure and 

 functions of the eyes of insects, Arachnida and Crustaceans; 

 an abstract of which can hardly fail to be of interest to 

 entomologists. 



It is well known that there are two rival theories as to the 

 manner in which the compound eyes of these animals perform 

 their function; the earlier, that of Johanes Miiller, pro- 

 pounded fifty years ago, which has had few supporters of late 

 years, is that each portion of the compound eye forms an 

 element o( the picture, the lenticular condition of the facet 

 being immaterial to its production ; only a straight ray of 

 light having the same direction as the tube which forms the 

 posterior ))art of the segment of the eye being utilised in the 

 production of the impression, each segment giving rise to a 

 single nerve stimulus only. 



The second theory is that each segment of the compound 

 eye produces a distinct inverted image of the object, just as 

 the simple eyes of insects, the eyes of vertebrates and other 

 animals do ; a view which originated in the well-known 

 experiment of Gottsche, who first showed the multiple 

 inverted images, which the facets of the cornea are capable 

 of producing, with the microscope. This theory has been 

 almost universally adopted, — amongst others by myself, — only 

 Boll and Leuckart having written in favoiu" of Muller's view ; 

 yet Dr. Grenacher has shown that the adoption of this view 

 has been too hasty, and that \\ith()ut any doubt Miiller was 

 right and his adversaries wrong. 



