48 SPIDERS [CH. 



Now the true spiders are always air-breathing, 

 and if they venture into the water at all they must 

 frequently come up to the surface to breathe, or else 

 they must store up a reservoir of air beneath the 

 surface of the water if they are to avoid death by 

 drowning. Nevertheless some of them have been 

 hardy enough to encroach on the domain of the 

 Crustacea. Not a few are able to run freely on 

 the surface of the water and even to dive occasionally 

 for the purpose of seizing one of its denizens, but the 

 number of those which have succeeded in really 

 adapting themselves to aquatic life is very limited, 

 and is, as far as we know, restricted to two small 

 groups, both of them members of the Agelenidae. 



Among the coral reefs of the Indian and Pacific 

 oceans, and also off the southern coast of Africa there 

 are found spiders of the genus Desis which spend 

 almost all their time under the surface of the sea, 

 from which they only emerge at low tide. They 

 construct very closely woven tents, impermeable to 

 sea-water, which imprison air at low tide, generally 

 choosing for the purpose some cavity which has been 

 excavated by one of the burrowing molluscs. Beyond 

 this we really know very little about them, and there 

 is much difference of opinion as to the mode in which 

 they obtain their food. Some writers state that they 

 only leave their shelters at low tide to chase small 

 crustaceans, and that when placed in vessels containing 



