THE WATEE SPIDER. 379 



learned that they were known under the name of Water 

 Spider {Argyronetra aqiuitica). 



This Spider is a most curious and interesting creature, because 

 it affords an example of an animal which breathes atmospheric 

 air constructing a home beneath the water, and filling it with 

 the air needful for respiration. 



The sub-aquatic cell of the "Water Spider may be found in 

 many rivers and ditches, where the water does not run very 

 swiftly. It is made of sUk, as is the case with all spiders' nests, 

 and is generally egg-shaped, having an opening below. This cell 

 is filled with air ; and if the Spider be kept in a glass vessel, 

 it may be seen reposing in the cell, with its head downwards, 

 after the manner of its tribe. The precise analogy between 

 this nest and the diving-bell of the present day is too obvious 

 to need a detailed account. How the air is introduced into the 

 cell is a problem that was for some time unsolved. The reader 

 is probably aware that the bubbles of air which are to be seen 

 on sub-aquatic plants are almost entirely composed of oxygen 

 gas, which is exuded from the plant, and which is so important 

 an agent in purifying the water. Some zoologists thought that 

 the air which is found in the cell of the Water Spider was 

 nothing but oxygen that had been exuded from the plant upon 

 which the nest was fixed, and that it had been intercepted in 

 its passage to the surface. In order to set the question at rest, 

 Mr. Bell, the well-known naturalist, instituted a series of ex- 

 periments upon the Spider, and communicated the resiilts to the 

 Linnean Society. The experiments were made in 1856, and 

 Mr. Bell's remarks are as follows : — 



" No. 1. Placed in an upright cylindrical vessel of water, in 

 which was a rootless plant of Stratiotes, on the afternoon of 

 November 14. By the morning it had constructed a very perfect 

 oval cell, filled with air, about the size of an acorn. In this it 

 has remained stationary up to the present time. 



" No. 2. Nov. 15. In another vessel, also furnished with 

 Stratiotes, I placed six Argyronetrae. The one now referred to 

 began to weave its beautiful web about five o'clock in the after- 

 noon. After much preliminary preparation, it ascended to the 

 surface, and obtained a bubble of air, with which it immediately 

 and quickly descended, and the bubble was disengaged from the 

 body, and left in connexion with the web. As the nest wa.s, 



