THE BRITISH SPONGES. 21 



mal construction of the base of the shell being altered 

 to suit the peculiarities of its habitation. There is in this 

 instance a foreseen relation between two very dissimilar 

 creations. The habitat of Balanus spongeosus, says Co- 

 lonel Montagu, is extremely curious: " it is found enveloped 

 or bedded in a particular species of sponge, exposing no- 

 thing but the points of the operculum." — " Amongst the 

 reticulated fibres of this sponge the Balanus finds a secure 

 lodgement in its infant state, and is soon enclosed by the 

 growing fabric of the sponge animal, except a small open- 

 ing, which is kept clear by the vortex occasioned by the 

 constant motion of the feelers or tentacula of the Triton in- 

 habiting the shell.'"* — But these are too trivial offices for so 

 large and widely spread a family, and probably the power 

 which its members possess of reducing to a solid condition 

 the horn, the silex and lime of the waters they live in, is 

 what constitutes their importance amongst rival entities, 

 and gives them a certain influence over the phases of this 

 ever-changing globe, — an influence which we shall certain- 

 ly underrate unless there are taken into account their vast 

 numbers and universal difiiision, — their size in more ge- 

 nial seas, — and above all their unceasing operation on the 

 waters, continued from a2:e to age without one moment's 

 intermission. That they were called early into existence 

 we know from the remains of them found in nearly the 

 earliest of fossiliferous rocks ; and the same evidence as- 

 sures us that they have never been without an heritable suc- 

 cession.f Thus the number and variet)' of their species in- 



Testacea Britannica, Supp. p. 3 

 t Sponges occur fossil in tlie tertiary, cretaceous, oolitic, perhaps in 

 the carboniferous, in the silurian, and probably in systems even older 

 than this. See Phillips' Treatise on Geology, i. p. 76. 



