THE ARACHNIDA, 447 
The engraving represents some of the spiders on the floating 
leaves, and one has made its plunge into the water. The cephalo- 
thorax is white, because the fine silky covering of web which 
encases the body contains air; and the whole of the spiders 
THE NESTS OF THE WATER SPIDER. (Argyroneta aquatica.) 
which are seen deep in the water are of the same colour, because 
air is mechanically entangled in the tissue covering the whole 
of their bodies. This air is rubbed off with the aid of the legs 
when the spider enters its bell-shaped nest, and its globules replace 
the water, and at last, after successive ascents and descents, the 
dome is full of air. 
