116 THE FAUNA OF THE DEEP SEA 



maintain itself almost unchanged through all the 

 countless generations that have elapsed since 

 Cambrian times, and can now flourish amid the 

 desperate struggle for existence in the shallow waters 

 of the tropics, while its companions, the corals, 

 mollusks, arthropods, &c., have changed or passed 

 away, is one of those problems in natural history 

 that seems to us impossible of solution. The time 

 may come when we shall be able to appreciate better 

 than we do now the complicated relations between 

 animals and their environment, and then perhaps the 

 peculiar fitness of Lingula will be made manifest ; 

 but at present we can but mention the fact as a fact, 

 and leave the solution of the problem to the future. 



The order Gephyrea is probably another very 

 ancient group of animals, although in the absence 

 of any hard calcareous, siliceous, or horny skeleton 

 the geological record can give us no confirmation of 

 their antiquity. As with the Brachiopods so with 

 the Gephyrea, some of the species have a very wide 

 bathymetrical distribution. Slpunculus nudus, for 

 example, the commonest and best known of all the 

 Gephyrea, extends from quite shallow water to a depth 

 of over 1,500 fathoms. As Selenka has pointed out, 

 it is those Gephyreans that live in holes in stones, or 



