ON ARACHNIDA. 469 



entirely. It is in the interior of these waters, and not at the 

 surface that it inhabits, differing in this respect from some 

 other species of aquatic spiders. We begin to find it from the 

 first warm days in spring. It swims in a reversed position, 

 having the under part of the body turned upwards ; its abdo- 

 men is then enveloped with a ball of air, and appears like a 

 little silvery and very brilliant globe. Degeer tells us that 

 the entire body, feet excepted, is involved in a globe of air. 

 This has not been verified by other observers to the same 

 extent. It often comes to the surface of the water, keeping 

 its body suspended there, the lower extremity upwards, ap- 

 parently for the purpose of respiration. We at present 

 know the place of the organs of respiration, and that they are 

 not spinnerets, as Clerk supposed. But how does it manage 

 to envelope a large portion of its body with this mass of air ? 

 what is the cause of its adhesion ? These are problems which 

 observation has not yet solved. 



A property of these araneides, not less singulai", is the 

 capacity of constructing for themselves, in the bosom of the 

 water, a kind of aerial mansion, a true diving bell, where they 

 can respire freely, live in safety, and which serves as a cradle 

 for their family. This may be compared to a diving bell, 

 not only because it has the same destination, but the same 

 form, namely, that of a cap, or that of one half of the shell of 

 a pigeon's egg. It is entirely filled with air, perfectly close, 

 the under part excepted, where there is a tolerably large 

 aperture, giving an entrance and exit to the animal. Its 

 walls are slender, and composed of a tissue of white silk, 

 strong, and close, a great number of irregular threads fix it 

 to the stems of plants, or other bodies. Sometimes the upper 

 part is out of the water, but most generally it remains entirely 

 immersed. Its inhabitant is thus environed with air ; she 

 remains there quietly, the head usually down, a situation 

 which permits her to see more easily what passes, to watch 



