32 
G. H. Parker 
liquid; and, when a number of cones are removed together, thougb 
tbeir outlines are at first distinguishable, they soon melt into an 
almost bomogeneous, transparent mass. This usually takes place 
also wben the retina is prepared according to Gottsche’s metbod, 
and thus a bomogeneous mass is produced by wbicb tbe images 
from tbe facets are simply displaced to a deeper region in tbe eye. 
As tbese images were not observed in preparations in wbicb tbe 
structure of tbe cones was unaltered, it seems to me tbat tbey must 
be regarded as functionally unimportant, and I account for tbem by 
tbe fact tbat one part of tbe dioptric apparatus, tbe facet, bas remained 
intact, wbile anotber part, tbe cone, bas been rendered ineffective 
by an alteration in its structure. 
Having reacbed tbe conclusion tbat tbe normal retinal Image is 
of such a cbaracter tbat eacb rbabdome receives only a single 
Impression, tbere still remains tbe question: Does tbe finer struc- 
ture of tbe rbabdome justify tbis conclusion? Granting tbe fibrillär 
structure of tbis body, it migbt be assumed tbat eacb fibrilla repre- 
sents an isolated perceptive organ, tbe wbole rbabdome tbus consti- 
tuting a perceptive field like tbe buman retina. Tbe distribution of 
tbe fibrillae, bowever, does not favor tbis view; for, wbetber we 
assume tbem to be effected by ligbt only at tbeir free ends or 
tbrougbout tbeir entire lengtb, tbey never present a mutual arrange- 
ment favorable for tbe reception of separate impressions. Tbe fact 
tbat tbe quarter-plates of fibrillae from one retinular cell alteruate 
vertically witb tbose from anotber so tbat tbe same kind of ligbt 
would effect botb sets of fibrillae, is* directly opposed to tbe idea tbat 
eacb rbabdome receives numerous separate impressions. In fact, tbe 
structure of tbe rbabdome seems admirably adopted for destroying 
precisely tbis difference. Viallanes (91a, pag. 396), bowever, assumed 
tbat eacb retinula represented seven perceptive Organs capable of per- 
ceiving eacb a single Impression. Witbout raising tbe question wby 
tbese seven elements are united to form a retinula, I believe we 
can grant wbat Viallanes Claims and still bave difficulties enougb 
to explain bow seven perceptive Organs, such as tbe retinular cells, 
can be very effective in perceiving an image such as tbat wbicb 
Viallanes believes to be tbrown on tbem. Tbe images figured by 
bim are altogetber too rieb in details for such a retina, and I side 
witb Grenachee (79, pag. 152) in tbe opinion tbat, if seven is tbe 
greatest number of separate perceptive elements tbat can be assumed 
for eacb retinula, it is more likely tbat tbe retinula receives only 
