28 
G. H. Parker 
brain, and that no other structure in tbe retina possesses both of 
these peculiarities , is strong evidence in favor of tbe perceptive 
nature of this body. Moreover, granting this conclusion, tbe cbanges 
undergone by tbe pigment become perfectly intelligible, for tbey are 
obviously directed toward Controlling tbe quantity and tbe quality 
of ligbt tbat reacbes tbe rbabdome. Tbese various reasons, I be- 
lieve, justify tbe conclusion tbat tbe rbabdome is tbe perceptive 
Organ of tbe retina. 
Having reacbed tbis point, tbere still remains tbe question con- 
cerning tbe cbaracter of tbe impressions made npon tbe rbabdomes: 
does eacb rbabdome perceive a complete picture or only one ele- 
ment in a picture? Tbis problem may be approacbed from two 
sides; we may first try to ascertain tbe cbaracter of tbe image 
tbrown on tbe rbabdome by tbe dioptric apparatus, and secondly, by 
examining tbe finer structure of tbe rbabdome itself, we may 
attempt to determine to wbat extent it is capable of perceiving an 
image. 
Concerning tbe cbaracter of tbe image tbrown by tbe dioptric 
apparatus, tbere are already a number of conflicting observations and 
opinions. From tbe time of Leeuwenhoek, investigators bave been more 
or less familiär witb tbe fact tbat eacb facet in tbe corneal cuticula is 
capable of projecting at a short distance bebind itself a small in- 
verted image of an object beld in front of it. In a carefully pre- 
pared fly’s eye, Gottsche (52, pag. 488) believed tbat this image 
was to be seen at tbe proximal end of tbe cone, and, regarding it 
as functionally significant, be raised tbe question of bow and where 
it is perceived. Max Schultze (68, pag. 27), wbo, as we bave 
already seen, correctly interpreted tbe rbabdome as tbe perceptive 
Organ of tbe retina, took tbe Suggestion from Zenker tbat tbe den- 
ser material of tbe proximal part of tbe cone-cells migbt cause a 
proximal displacement of one of tbe foci of tbe dioptric apparatus, 
and believed tbat in tbis way an image migbt be tbrown on tbe 
rbabdome. Viallanes (92, pag. 372) States tbat, in tbe eyes of 
insects and crustaceans prepared by a metbod essentially similar to 
Gottsche’s, a small inverted image could be observed at tbe distal 
end of eacb retinula. It is, tbeu, a matter of Observation tbat for 
eacb ommatidium in . freshly prepared eyes a small inverted image 
occurs not far from tbe distal end of tbe rbabdome. 
These observations are directly opposed to those of Exner (91), 
wbo, after preparing tbe ratber resistant dioptric apparatus of Lam- 
