110 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 
tion and movements are largely determined by the in- 
fluences received through the feelers and the eyes. These 
receive their nerves from the cerebral ganglia; and, as 
might be expected, when these ganglia are extirpated, 
the crayfish exhibits no tendency to get away from the 
light, and the feelers may not only be touched, but 
sharply pinched, without effect. Clearly, therefore, the 
cerebral ganglia serve as a ganglionic centre, by which 
the afferent impulses derived from the feelers and the 
eyes are transmuted into efferent impulses. Another 
very curious result follows upon the extirpation of the 
cerebral ganglia. If an uninjured crayfish is placed upon 
its back, it makes unceasing and well-directed efforts to 
turn over; and if everything else fails, it will give a 
powerful flap with the abdomen, and trust to the chapter 
of accidents to turn over as it darts back. But the 
brainless crayfish behaves in a very different way. Its 
limbs are in incessant motion, but they are “ all abroad ;” 
and if it turns over on one side, it does not seem able 
to steady itself, but rolls on to its back again. 
If anything is put between the chele of an uninjured 
crayfish, while on its back, it either rejects the object at 
once, or tries to make use of it for leverage to turn over. 
In the brainless crayfish a similar operation gives rise to 
a very curious spectacle.* If the object, whatever it be 
* My attention was first drawn to these phenomena by my friend 
Dr. M. Foster, F.R.S., to whom I had suggested the desirableness of 
an experimental study of the nerve physiology of the crayfish, 
