1886. | Microscopy. 203 
ing to desire. My experiments with these eggs have not yet 
been carried very far, and I can only say that the material, so far 
as examined, has turned out well. If the sectioning is not delayed 
too long, no disagreeable effects of crumbling will be experienced. 
—C. O. Whitman. 
Tue Funcrion oF THE Compounp Eve.—It is held by Exner, 
Carriére, and others that the compound eye does not distinguish 
the forms, but only the movements of objects. The eye would 
thus be merely an organ of orientation, capable of recognizing 
differences in the intensity of light. Plateau! has undertaken a 
series of interesting experiments designed to test the validity ot 
this view. The method of experimentation was as follows: 
A room five meters square is furnished with two windows, 
which face the west. The windows are provided with shutters, 
by means of which the room can be made dark. In each shutter 
a hole is cut large enough to receive a pane of ground glass. 
The vertical distance from the floor to the center of each glass is 
1.75" and the horizontal distance between the centers of the two 
panes is 2.30" The amount of light admitted is regulated by 
large opening, but the amount of light that passes the former is 
considerably less than that which passes the latter. In successive 
experiments with different diurnal insects (Diptera, Hymen- 
-optera, Lepidoptera, Coleoptera, &c.), the size of the hole in the 
le diaphragm is varied, so that the amount of light is sometimes 
greater, sometimes less than that of the right diaphragm. 
If, under these conditions, an insect let loose at the side of the 
room opposite the windows, invariably flies to the large opening, 
then „we might conclude, according to Plateau, that it dis- 
tinguishes the forms of objects; but if it often makes the mis- 
sga of flying against the surface perforated with holes too small 
ee Bes it passage, we may conclude that it does not distinguish 
‘lass ut is guided by the intensity of the light. The experiments 
Show that the flight is directed, in the majority of cases, towards 
more intense light, and hence Plateau concludes that the 
Bull. de P Acad. roy. de Belg., 3™¢ sér. t. x, No. 8, 1885. : 
