CHAPTER I. 
APPLICATION OF THE FOREGOING PRINCIPLES TO THE 
LOWEST ANIMALS. 
Protozoa . 
No one can have watched the movements of certain 
Infusoria without feeling it difficult to believe that these 
little animals are not actuated by some amount of intelli- 
gence. Even if the manner in which they avoid collisions 
be attributed entirely to repulsions set up in the currents 
which by their movements they create, any such mechanical 
explanation certainly cannot apply to the small creatures 
seeking one another for the purposes of prey, reproduction, 
or, as it sometimes seems, of mere sport. There is a 
common and well-known rotifer whose body is of a cup 
shape, provided with a very active tail, which is armed at 
its extremity with strong forceps. I have seen a small 
specimen of this rotifer seize a much larger one with its 
forceps, and attach itself by this means to the side of the 
cup. The large rotifer at once became very active, and 
swinging about with its burden until it came t o a piece of 
weed, it took firm hold of the weed with its own forceps, 
and began the most extraordinary series of movements, 
which were obviously directed towards ridding itself of the 
encumbrance. It dashed from side to side in all directions 
with a vigour and suddenness which were highly astonish- 
ing, so that it seemed as if the animalcule would either 
break its forceps or wrench its tail from its body. No 
movements could possibly be better suited to jerk off the 
offending object, for the energy with which the jerks were 
given, now in one direction and now in another, were, as I 
have said, most surprising. But not less surprising was 
