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 singular, 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 halt 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 
