246 MILDRED HOGE RICHARDS AND ESTHER Y. FURROW. 



meres. Indentations in this protoplasmic ring reveal the 

 position of the boundaries of the retinula?. Each retinula has, as 

 the cross sections indicate, a nucleus at the distal end just below 

 the nucleus of the cone cell. Nuclei were also observed at the 

 proximal end of the retinula?, although we were not able to 

 determine with accuracy whether each one has a nucleus at this 

 level. 



Pigment cells separating the ommatidia were distinguished in 

 both longitudinal and cross sections. These separate the cone 

 cells and the retinula? of the neighboring ommatidia. Since the 

 pigment cells did not seem to have a practical bearing on our 

 problem, no attempts were made to demonstrate them with 

 special methods by which a more complete study of them would 

 be possible. 1 Hence the drawings do not include them. 



The eye is connected to the brain by a series of three ganglia 

 which we will call the outer, median, and inner; these correspond 

 to the same ganglia named by Hickson from the outside inward 

 as periopticon, epiopticon, and opticon respectively. The outer 

 ganglion joins at its distal edge the basement membrane and is 

 flattened out to conform to the shape of the eye. Centrally it 

 narrows passing into nerve fibers which decussate to enter the 

 median ganglion (Plate II., Fig. i). The median and inner 

 ganglia have each the shape of a meniscus lens in transverse 

 sections. From the median ganglion fibers pass to the inner. 

 The inner ganglion is connected to the brain by short fibers 

 which do not seem to cross. There is thus no optic nerve as in 

 crustaceans, a fact long ago pointed out by Berger. 



A more detailed study of the outer ganglion (Plate I., Fig. 5) 

 shows that it consists in its proximal part of nerve fibers arranged 

 in groups in parallel fashion. These groups constitute the 

 elements of the outer ganglion. In the distal part among cells 

 which do not seem to be uniformly arranged are scattered 

 tracheal vessels and groups of fibers which reach to the basement 

 membrane. The connections between these fibers and the 

 elements of the ganglion could not be followed in our sections. 



When the heads of eyeless flies were studied certain facts 



'While this paper was in proof, a study by O. A. Johannscn, entitled "Eye 

 Structure in Normal and Eye-Mutant Drosophilas " appeared: Jour. Morph. 

 Vol. 39, no. 2. Dec. 1924. The pigment cells are treated in detail in this work. 



