40 



LIFE, IN ITS LOWEIt FORMS. 



emulating the entangled twigs of a thorny bush in their 

 inelastic stiffness. But more commonly the slenderness 

 and arrangement of the fibres impart to the Sponge that 

 elasticity which is one of its most valuable qualities. 



In order to apprehend truly the character of any Sponge, 

 it should be examined alive if possible ; but if this be im- 

 practicable, at least specimens should be selected which 

 have been dried as they came from the sea, without hav- 

 ing been subjected to any processes of washing, pressing, 

 or cleansing. In specimens of Turkey Sponge in this 

 condition, Mr Bowerbank finds the horny fibres surrounded 

 by a beautiful tissue of branching vessels in great abun- 

 dance, enclosed in an external membrane or sheath. This 

 tissue Mr Busk has succeeded in injecting with coloured 

 fluid. 



The fibres are also covered with a web of darker colour 

 than their substance, composed of minute granules, which 

 are conjectured to be incipient gemmules ; for nucleated 

 gemmules were found on the fibres of other specimens, in 

 which the granulose texture was wanting. The macera- 

 tion in fresh water, however, and the immersions in 

 diluted acid to which the commercial Sponges are 

 subjected, remove the whole of the gelatinous flesh, and 

 render this structure inapparent in specimens sold in the 

 shops. 



In commerce two kinds of Sponge are known — the Tur- 

 key and the West Indian. But of the former Mr Bower- 

 bank makes two species, undistingnishable indeed by any 

 marks that the naked eye can appreciate, but recognised in 

 an instant on microscopical examination, by the presence 

 or absence of the investing vascular tissue above men- 



