40 
LIFE, IN ITS LOWER 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 tiro 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, removo 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, undistinguishable 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- 
