ANIMAL BEHAVIOR. 293 



c. Sensitiveness to LigJit. 



The question as to how much intelligence, if any, Clepsine 

 may have, I do not here undertake to settle or discuss. That 

 the animal is endowed with keen sensibilities is evident from the 

 behavior before described. The following simple experiment 

 affords a striking demonstration : Pass the hand over a dish in 

 which a number of Clepsines are resting quietly on the bottom, 

 at a distance of a few inches above the animals, taking care not 

 to make the least jar or other disturbance. If the animals are 

 quite hungry, the slight shadow of the hand, imperceptible 

 though it be to our eyes, will be instantly recognized by them, 

 and a lively scene will follow, every leech rising up, sup- 

 ported on its posterior sucker, and swinging at full length 

 back and forth, from side to side, round and round, as if in- 

 tensely eager to reach something. Put a turtle in the dish and 

 see what a scramble there will be for a bloody feast. The 

 shadow of the hand was to these creatures like the shadow of 

 a turtle swimming or floating over them in their natural haunts, 

 and hence their quick and characteristic response. A piece of 

 board floating over them would have the same effect. Although 

 so sensitive to a small difference in light, the Clepsine eyes can 

 give no pictures, and hence there is no power of visual discrimi- 

 nation between objects. They probably recognize their right 

 host by the aid of organs of taste ; at any rate they are often 

 able to distinguish their host from closely allied species. 



Instinct of Rolling into a Ball among Insects. 



The following examples of the instinct of rolling into a ball 

 among insects are from Kirby and Spence.^ 



" I possess a diminutive rove-beetle {Aleochara complicans 

 K. Ms.), to which my attention was attracted as a very minute, 

 shining, round, black pebble. This successful imitation was 

 produced by folding its head under its breast, and turning up its 

 abdomen over its elytra, so that the most piercing and discrimi- 

 nating eye would never have discovered it to be an insect. I 



1 Entomology, pp. 411, 412. 



