THE LIVING STRUCTURES 139 



color at will, space will not permit going into details. In 

 their place in life, the struggle for existence is fierce and 

 competition very strong, and they have also discovered 

 nearly every trick and method used by fishes and animals. 



The following article by A. L. Hodges states the situ- 

 ation in a general way: "Few people are familiar with 

 the fact that the diving bell was invented by a spider. 

 Such however is the case and if it was not actually in- 

 vented by him it was certainly used by him long before 

 our hydraulic engineers made one for the same purpose. 

 The diving bell is, as is well known, a cup-shaped body 

 with open end down which is let into the water. The air 

 is caught in the bell and keeps the water from rising 

 beyond a certain level at any specified depth and of course 

 allowing anyone inside to breathe and act as if he were 

 on the ground. The new improvement of the diving bell, 

 known as the Caisson, is a huge pipe which has compart- 

 ments into which the air is pumped from above. The 

 spider's bell is filled more in this manner than in the 

 other. 



"The name given to these little spiders is very appro- 

 priate Naiads of the family of Arachnida. The Naiad 

 will build a little house of water-proof silk, held fast by 

 strands fixed to neighboring blades of grass and stones, 

 several feet under water. He completes the entire struc- 

 ture before filling it with air as if he knew that the air 

 would tend to make it rise to the top and thus hinder the 

 attaching of the anchors. 



"But the method of getting air into their houses is per- 

 haps the most peculiar and interesting of all instinctive 

 acts of animals. Their abdomens are so made that a 

 bubble of air can be caught underneath them. This the 

 Naiad does, and swims to his house with it and turns it 

 loose in the airy structure. The process is repeated sev- 



