20 THE BRITISH SPONGES. 



to be ruled by the same influences ; while they run coun- 

 ter, says Laniouroux, to sea-weeds which cover in profusion 

 the bottom of the icy seas of the two poles. * I know not 

 on what data the Professor of Caen has grounded these 

 general remarks. Of the numerous species arranged under 

 the genus Sponc/ia by Lamarck 5 1 are said to grow in the 

 Australasian seas or on the shores of New Holland, 22 in 

 the Indian Ocean, 4 only in the Red Sea, 9 in the Medi- 

 terranean, 14 on the American coast, and 9 in the seas of 

 Europe, t It is too obvious that no conclusions of the 

 slightest value can be drawn from these imperfect lists, and 

 the geography of the sponges must for long remain a field of 

 exploration and discovery, for before it will yield any fruit, 

 either to the naturalist or geologist, the species must be all 

 re-examined with a care not yet bestowed upon them, so 

 that they may be referred to their proper genera, and those 

 of every zone made to exliibit their mutual resemblances 

 and discrepancies. 



What special uses sponges perform in the economy of 

 creation has been little enquired into. It would appear that 

 they are not made the food of any other tribe of animals ; 

 and the shelter wliich they give to some shell-fish, crabs, 

 and worms is accidental, or without any appropriated adap- 

 tation. There are a very few exceptions. Thus Mr Hogg 

 has discovered a very singular insect (Branchiotoma spon- 

 gillcB, Westwood,) which has not been detected in any 

 other situation than in the cells of the fresh-water sponge ; \ 

 and some marine Cirripedes or acorn-shells, — the Acas- 

 t(e of Leach, — nestle habituallv in a sponge, — the nor- 



• Polyp. Coral. Flex. p. 16. 



f Anim. s. Vert. 2de edit. ii. p. 542—57.3. 



f Lin. Trans, xviii. p. 390-1. 



1 



