1895.] NATURAL SCIENCES OF PHILADELPHIA. 161 



AN ARRANGEMENT OF THE RETINAL CELLS IN THE EYES OF FISHES 

 PARTIALLY SIMULATING COMPOUND EYES. 



BY JOHN A. RYDER. 



The peculiar structure of the compound eyes of the Arthropods 

 has attracted a large share of atteutiou from such investigators as 

 Grenadier, Lankester, Watase, Patten, Carriere and others. The 

 peculiarities of structure of compound eyes are so marked that it 

 would be strange if they failed to attract the notice of students of 

 morphology. In the vertebrates the structure of the retina is 

 universally regarded as differing so widely from that of the com- 

 pound type of eye found iu the Arthropods, that few authors have 

 been tempted to institute any very close morphological comparison 

 between them. • I should not attempt such a comparison were 

 it not that I have recently found that in the eye of the larval 

 salmon, Salmo salar, there is an arrangement of the sensory cells of 

 the retinal epithelium that is so regularly and definitely repeated 

 throughout the whole extent of the retina as to admit of no question. 



The observations . upon which my statements rest were made 

 upon certain very thin sections of recently hatched salmon larvae. 

 These sections were prepared for an entirely different purpose, and 

 it was only upon casual observation that the peculiarities I am about 

 to describe were first noticed. 



These sections ranged from 2. 5 to 5 mikrons in thickness, and no 

 doubt can be thrown upon my observations on the score of faulty 

 technique. The specimens had been splendidly fixed and preserved 

 and were stained in toto in an alcoholic solution of hematoxylin, 

 and differentiated in toto in a one per cent, solution of potassium 

 bichromate. This method leaves but little to be desired for clear- 

 ness of histological differentiation and sharpness of detail. Unfor- 

 tunately, it is only a very few sections out of a complete series that 

 reveal the details that are to be described. These few sections are 

 the first three or four that were cut tangentially to the surface of the 

 retina, and that which is cut just through the ends of the rods and cones 

 and cone- cells, at about the level of the inner or under side of the 



