THE WATER BOATMAN. 249 



tating to the senses as that of a slate pencil when held 

 by an awkward child. 



Now, the natural oar of the insect has its grease- 

 pot as well as the artificial oar of the human being. 

 The joints, especially the principal one at the thorax, 

 are lubricated with a natural grease exactly analogous 

 to the " synovia/' or oily fluid, which diminishes the 

 friction in the joints of human beings. It is worthy 

 of notice, too, that in artificial machinery man has to 

 imitate the absolutely perfect machinery of nature. 

 I have always thought, when looking at a steam- 

 engine at work, and seeing the oil-cups above each 

 important part, that the engineer was only executing 

 a clumsy imitation of nature, and that the greatest 

 engineer of coming times would be a man who was 

 versed in the anatomy of the human frame. 



The air which serves the purpose of respiration 

 while it is beneath the surface, is carried between the 

 wing-cases and the body, exactly as has been narrated 

 of the water beetle. Fortunately for observers of 

 nature, the wing-cases are sufficiently translucent to 

 enable the progress of the air to be seen through 

 them. I believe that I was the first to describe this 

 progress, through actual observation of some Water 

 Boatmen that I kept in an aquarium. 



The discovery was quite a matter of accident. I 

 had been keeping some Water Boatmen in a bottle 

 which was standing on my desk, and happened to get 

 one of the insects between the eye and the light. 

 The translucent character of the elytra at once was 

 evident, and the course taken by the air was perfectly 

 visible. 



