THE WATER-SPIDER 271 



nearly its whole life submerged. In order to do this 

 without interruption to its breathing, the spider carries 

 down a bubble of air, which overspreads the whole abdomen 

 as well as the under side of the thorax. These parts of the 

 body are covered with branched hairs, so fine and close 

 that the surface-film cannot pass between them. The 

 spider swims on its back, and the air lodges in the neighbour- 

 hood of the respiratory openings, which are placed on 

 that surface which floats uppermost. When the spider 

 comes to the top, as it does from time to time to renew 

 its supply of air, it pushes the abdomen out of the water, 

 and we can then see that this part of the body is quite 

 dry. When it sinks, the water closes in again at a little 

 distance from the body, and the bubble forms once more. 



It would be inconvenient to the water-spider to be 

 obliged to come frequently to the surface for the purpose 

 of breathing. A predatory animal on the watch for its 

 victims must lie in ambush close to the spot where they 

 are expected to appear, and the water-spider accordingly 

 requires a lurking-place filled with air, beneath the surface 

 of the water. It has its own way of supplying this want. 

 Relying on the fact that the surface-film of water will 

 not readily pass through small openings, the spider pro- 

 ceeds as follows. It begins by drawing together some 

 water-weeds with a few threads, in such a way that they 

 meet at one or more points. It then fetches from the 

 surface a fresh supply of air, and squeezes part of it out 

 by pressing together the bases of its last pair of legs. The 

 bubble rises, but is detained by some of the threads pre- 

 viously spun across its path. Then the spider returns to 

 the surface to fetch another bubble, and repeats the opera- 

 tion as often as may be necessary. Now and then she 

 secures the growing bubble by additional threads, and 

 before long has a bubble nearly as big as a walnut inclosed 

 within a silken invisible net, which imprisons the air as 

 effectually as a dome of glass would do. The spider takes 

 care to conceal her home from observation, and before long 



