THE BRITISH SPONGES. 7 



for, as Professor Grant has remarked, " the odours of some 

 sponges are decidedly animal, while others belong to com- 

 mon and well-known vegetables. The Spongia coalita, 

 when newly taken from the water, smells very strongly of 

 the common mussel, and Avhen burnt, it still resembles the 

 same bivalve burnt ; the Spongia compressa, on the other 

 hand, smells strongly of the common mushroom ; some, as 

 the Spongia oculata, have scarcely a perceptible odom\" * 

 The composition of the skeleton or fibrous portion of the 

 sponge is remarkably diversified, but in this sketch I limit 

 myself to a notice of the variations exhibited in our typical 

 native species. In the true sponges (^Sj)ongia) the fibres 

 which bound the intercellular spaces are horny smooth 

 subcylindrical threads, of unequal tliickness, and, accord- 

 ing to Ellis and Grant, tubular throughout, so that the con- 

 tinuity of the canal is uninterrupted even at the junctions 

 or anastomoses of the net-work ;t but Dujardin and Mr 

 Bowerbank have proved that this is an erroneous descrip- 

 tion of the structure, for the thi-ead is in fact solid and im- 

 perforate.| (Fig. 3.) The fibres of other sponges {Hali- 

 chondria) are formed of slender crystalline spicula compos- 

 ed of silex or flint in a pure state, laid in a not over-exact 

 parallelism, and bound together by a substance analogous 

 to horn or albumen ; but there are many species of Hali- 

 chondria in which this albuminous matter is diffiised, so 

 that the fibrous structure has become obscure, and the spi- 

 cula, now predominant, lie crossed in every direction and 



* Edin. Phil. Jourri. xiii. p. 96. 



f Ellis and Soland. Zooph. p. 184 : Grant in Edin. Phil. Journ. xiv 

 p. 340. 



\ Microscopic Journal, i. p. 10, Annals Nat. Hist. vii. p 73. 



