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SYDNEY J. HICKSON. 
According to this view then, the pseudocone is a space filled 
with a fluid or semi-fluid substance situated between the cornea 
and the “ Semper’s nuclei.” 
In Musca this space is seen to be traversed by four very 
delicate clear bands passing from the innermost regions of 
the pseudocone to the facet. (Grenacher, p. 90, figs. 63, 
64, Ps. C.). 
There can be no doubt now, I think, that these bands do not 
exist as such in the living eye, but that their appearance is due 
to the action of reagents. I have found them in a similar 
position in Eristalis, and I am led to believe that they 
represent the shrivelled remains of the external part of the 
cone-cells. 
This portion of the cone-cell I believe to be filled in the 
living condition with a fluid or semifluid substance which 
performs the same function as the crystalline cone of the 
“ eucone eyes/’ but that it is partially or wholly dissolved by 
reagents and only the cell walls, and perhaps part of the proto- 
plasmic cell substance are left in the form of four bands 
passing through the space formerly occupied by the pseudocone. 
The inner part of the cone-cells containing four nuclei 
(‘ Semper’s nuclei ’ Grenacher) are seen at the base of the 
pseudocone in close contact with the end of the rhabdom. 
The development of the crystalline cone has been carefully 
investigated by Claparede (5), and he shows that it is developed 
in four pieces in the primitive cone-cells (Krystallzellen) on 
the inner side of the nuclei, that each part increases in size 
until it forms with the three others the crystalline cone by 
apposition. In the adult condition the crystalline cone is with 
difficulty divisible into its four constituent parts, and the nuclei 
of the cone-cells remain as the “ Semper’s nuclei ” of the adult. 
From my own researches upon the developing bee and cock- 
roach. I believe this to be a very fair statement of what 
occurs. The structure of the adult crystalline cone may be 
very well studied in Aeschna grandis (figs. 12 and 13) in 
which the “ Semper’s nuclei ” are seen to be large, well marked, 
and usually situated in the four corners of the quadrangular 
