OBSERVATIONS ON INSECT LIFE 173 



of anything that has occurred. The glass intercepts 

 the surface vibrations of the water ; it cannot affect 

 the boatman's vision. The boatman can well appre- 

 ciate the direction from which the vibrations come. 

 I approach one with a needle and touch the water 

 with the point. The boatman is aroused but it does 

 not act aimlessly ; it first turns about so as to face 

 the point where the needle touches the water before 

 making its unerring stroke. This tactile sense is 

 exquisite. The boatman is not disturbed by vibrations 

 other than surface tremors. It is not misled by the 

 ripples of the wind. I tap the sides and bottom of 

 the basin, but this will not excite the insect. Visible 

 ripples may flow across the basin, but the boatman 

 is not deceived. I will mention a more remarkable 

 instance as a proof of the nicety of this tactile sense, 

 I drop some fragments of cork into the basin, and the 

 boatmen, feeling the vibrations, instantly spring upon 

 them. I allow the same pieces of cork to strike the 

 surface by floating up through the water from below, 

 and the boatman takes no notice. In both cases the 

 surface vibrations spread over the surface of the water. 

 In one the contact is from above, in the other from 

 below, and the boatmen can discriminate between 

 them. 



It seems most probable that it is on one of the 

 parts of the insect in contact with the surface of 

 the water that the sensitive organs of touch will be 

 developed. Those parts are the tarsi of the first two 

 pairs of limbs and the tip of the abdomen. Now just 

 at the base of the claws of the intermediate tarsi there 

 is a specialized tuft of delicate hairs, and I have 

 thought that these might have been the highly sensitive 



