32 
G. H. Parker 
liquid; and, wlien a number of cones are removed together, though 
their outlines are at first distinguishable, they soon inelt into an 
almost liomogeneous, transparent mass. This usually takes place 
also when the retina is prepared according to Gottsche's method, 
and thus a homogeneoiis mass is produced by which the images 
from the facets are simply displaced to a deeper region in the eye. 
As these images were not observed in preparations in which the 
structure of the cones was unaltered, it seems to me that they must 
be regarded as functionally unimportant, and I account for them by 
the fact that one part of the dioptric apparatus, the facet, has remained 
intact, while another part, the cone, has been rendered ineffective 
by an alteration in its structure. 
Having reached the conclusion that the normal retinal image is 
of such a character that each rhabdome receives only a single 
Impression, there still remains the questioni Does the finer struc- 
ture of the rhabdome justify this conclusion? Granting the fibrillar 
structure of this body, it might be assumed that each fibrilla repre- 
sents an isolated perceptive organ, the whole rhabdome thus consti- 
tuting a perceptive field like the human retina. The distribution of 
the fibrillae, however, does not favor this vievr; for, vrhether we 
assume them to be effected by light only at their free ends or 
throughout their entire length, they never present a mutuai arrange- 
ment favorable for the reception of separate impressions. The fact 
that the quarter-plates of fibrillae from one retinular cell alternate 
vertically v^ith those from another so that the same kind of light 
would effect both sets of fibrillae, is directly opposed to the idea that 
each rhabdome receives numerous separate impressions. In fact, the 
structure of the rhabdome seems admirably adopted for destroying 
precisely this difference. Viallanes (91a, pag. 396), hovs^ever, assumed 
that each retinula represented seven perceptive organs capable of per- 
ceiving each a single Impression. Without raising the question why 
these seven Clements are united to form a retinula, I believe we 
can grant what Viallanes claims and still have difficulties enough 
to explain how seven perceptive organs, such as the retinular cells, 
can be very eifective in perceiving an image such as that which 
ViALLANES believes to be thrown on them. The images figured by 
him are altogether too rieh in details for such a retina, and I side 
with Geenacher (79, pag. 152) in the opinion that, if seven is the 
greatest number of separate perceptive Clements that can be assumed 
for each retinula, it is more likely that the retinula receives only 
