172 A NATURALIST IN HIMALAYA 



and have their beinof." The moment the tiniest insect 

 falls on the water the boatman is instantly aware of 

 the surface vibrations and darts like lightning on its 

 prey. 



A few experiments will soon make evident this 

 delicate sense of touch. I place some boatmen in a 

 basin of water ; they swim about content. I approach 

 one with the point of a fine needle. It takes no 

 notice. I bring the needle so as almost to touch the 

 boatman, but it excites no sense and the boatman 

 hovers on. I lower the point till it touches the water. 

 The boatman is instantly aroused ; it springs forward 

 on the needle. The sense of touch through contact 

 with the water stimulates the insect. It would not be 

 so foolish as to dart upon a needle had vision been its 

 guide. But it is easy to make still more certain that 

 it is touch and not sioht which cjuides the boatmen to 

 their prey. I stand a glass tumbler in a basin of 

 water. I pour water into the tumbler until it reaches 

 the same level as the fluid outside. I now place six 

 boatmen in the basin and they swim about content. 

 I throw them some insects ; the boatmen dart on 

 them, plunge beneath the surface to drown and 

 devour them. At a distance of six inches they feel 

 the prey touch the water and dash forward to the 

 capture. I now throw some insects into the tumbler. 

 They fall on the water standing at the same level as 

 the water in the basin. The boatmen are swimming 

 outside ; the insects fall within the glass. The insects 

 fall close to the boatmen, but the glass intervenes and 

 the boatmen take no notice. I throw an insect into 

 the orlass when the boatman is on the water outside 

 not half an inch away, but it remains quite oblivious 



