(¢ lyi-) 
marble in the picture formed in the insect’s eye; if so, I 
have not met with it: indeed, I may say, in passing, that 
Grenacher devotes the larger part of his chapter on the 
function of vision to demolishing the theories of others,— 
that is to say, showing how insects do not see,—and when 
he comes to the positive aspect, confines himself to some 
vague generalities; but, though it may be the case that the 
lines of separation in the mosaic would be very fine, yet they 
would be very numerous, and I wish to urge that their 
existence, taken in conjunction with the immobility of the 
insect’s eye, appears to me absolutely to destroy what little 
value the flat-picture without secondary adjuncts might other- 
wise possess. In point of fact, in order to see anything, the 
insect must come to a dead standstill, for to a moving insect 
with a fixed eye the lines of interruption of the mosaic would 
appear to move, and cause the flat-picture to become a com- 
plete blur. I attach considerable importance to this con- 
sideration, because we know that the compound eye attains 
its highest perfection in insects with great powers of flight,— 
in other words, that the compound eye is a guide during rapid 
motion. Now let me ask you to recall that when we our- 
selves are in movement it is a great obstacle to the satis- 
factory exercise of our function of picture-seeing; indeed, 
when we are in rapid motion, we can only see at all by 
keeping up a constant movement of the eye, so as to counter- 
act the motion of our body, and this causes such fatigue that 
the effort to look at near objects, amongst which we are 
moving, cannot be for long carried on. How, then, can an 
insect in motion, with two separate and different flat pictures 
in its fixed eyes, each picture blurred by the passage across 
it of the lines of cement in the mosaic, guide itself with the 
absolute perfection it actually exhibits? Taking all the above 
points into consideration, I think mosaic vision for insects 
must be relegated to that domain where first attempts 
towards elucidating very difficult subjects generally go. And 
I think we may go farther than this and view any theory of 
flat-picture vision for insects with very great suspicion. 
This conclusion almost renders it unnecessary to discuss 
in detail some of the other theories that have been put 
