248 POPULAR HISTORY OF THE AQUARIUM. 



live principally under water, but come out to change their 

 skin, and at times, also, to chase terrestrial insects, which 

 thej drag beneath the surface as soon as caught. 



The most curious circumstance connected with these 

 Water-Spiders is the manner in which they construct nests 

 under the water, for residence, and for the deposition of eggs, 

 and fill them with air brought from the surface. 



In constructing its nest the Argijroneta rises to the sur- 

 face, and, with its head downwards, places the point of its 

 abdomen in contact with the external air. Expanding the 

 filaments at that point, it encloses, in ag lin sinking, a small 

 bubble of air, which it retains in a rounded form, indepen- 

 dent of the bubble which covers the rest of its abdomen. It 

 then swims towards the edge of the plant to which the nest 

 is to be attached, and touches the little bubble in such a 

 manner as to make it leave its own body, and adhere to the 

 edge of the plant. The Spider again mounts, brings down 

 another bubble, and so on in succession, until he has a 

 mass of small bubbles collected, around which he then 

 begins to spin a web, by means of which he brings the se- 

 parate bubbles together, so as to form a single one large 

 enough to contain his body. Living afterwards in this 

 little balloon, the Spider spreads filaments round the aper- 



