70 General Notes. [January, 
consists mainly in the perception of movements. He enumerates, 
in support of his thesis, a series of important facts. In man the 
power of plainly distinguishing forms only belongs to the cen- 
tral part of the retina, while we perceive movements very well by 
the aid of the peripheral region of this sensitive layer. 
Most animals, both vertebrates and invertebrates, seem but 
little impressed by the form of their enemies or of their victims, 
but their attention is immediately excited by the slightest dis- 
placement. Hunters, fishermen and entomologists have made in 
this respect numerous and demonstrative observations, 
Finally, though the production of an image in the facetted eye 
of the insect or the crustacean seems impossible, we can easily 
conceive how the Arthropod can ascertain the existence of a 
movement. Indeed, if a luminous object is placed before a com- 
pound eye, it will illuminate a whole group of simple eyes or 
facets; moreover the centre of this group will be clearer than the 
rest. Every movement of the luminous body will displace the 
center of clearness; some of the facets not illuminated will first 
receive the light, and others will reénter into the shade; some 
nervous terminations will be excited anew, while those which 
were so formerly will cease to be. 
In résumé, careful physiologists, relying on the structure of the 
compound eyes of Arthropods, admit that these animals do not 
see the form of objects, but only perceive colors and movements. 
Their facetted eyes are not complete visual organs, but simple 
organs of orientation. 
Plateau then details the experiments he made to determine this 
question ; and which we cannot well abstract. He calls attention 
to one result of his experiments: that insects only utilize their 
eyes to choose between a we luminous orifice in a dark cham- 
ber, or another orifice, or group of orifices, equally white. They 
are guided neither by odorous emanations, nor by differences of 
color. A fact which will certainly astonish all entomologists and 
likewise surprise the experimenter himself is, that bees have as 
bad sight and comport themselves almost exactly as flies. 
From numerous experiments on Diptera, Hymenoptera, Lepi- 
doptera, Odonata and Coleoptera, Plateau comes provisionally to 
the following conclusions: 
1. Diurnal insects have need of a quick, strong light, and can- 
not direct their movements in partial obscurity. ‘ 
2. In diurnal insects with compound eyes, the simple eyes offer 
so little utility that it is right to consider them as rudimentary 
‘ensity as well as by the apparent excess of 
surface. In short, they do not distinguish the form of objects, or, 
if they do, distinguish them very badly. 
