THE EYE AND OPTIC TRACT OF INSECTS. 
215 
The Eye and Optic Tract of Insects. 
By 
Sydney J. Hickson, B.A. Cantab.. D.Sc. Conti., 
Scholar of Downing College, Cambridge, and Assistant to the 
Linacre Professor of Comparative Anatomy at Oxford. 
With Plates XV, XVI and XVII. 
The structure of the eyes of the Arthropoda has been a 
favourite subject with morphologists for many years, and many 
beautiful monographs have been published detailing the results 
of the careful observations that have been made upon this 
subject. Until the last few years the observations stopped 
short at the basilar membrane, and the tract lying between the 
percipient elements and the brain remained unknown. Of late 
years, however, several papers have appeared dealing with the 
optic tract and its relations to the eye proper, or ommateum 
(Lankester and Bourne), and as some of these have attempted 
to throw doubts upon what were formerly considered to be 
well-founded homologies, I have gathered together in this 
memoir some of the most interesting results of the researches 
I have been carrying on for the last two or three years with 
the hope of being able thereby to throw some light upon these 
obscure or disputed points. In order to make my memoir 
more complete I have carefully revised the structure of the 
ommateum itself in Musca vomitoria, and I shall here 
give a detailed account of it based upon my own observations 
before I proceed to describe the nervous elements which connect 
it with the brain. 
The descriptions which have been published of the ommateum 
of insects in general and Musca in particular, are now so 
VOL. XXV. NEW SER. 
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