96 Dr Grant’s Observations on the Structure and 
times do not exceed half an inch when full grown, while the 
splendid Spongias crateriformes of tropical seas, are known to 
acquire a magnitude of nearly four feet. And probably spon- 
ges acquire a much greater size when they spread over the 
sheltered surface of cliffs in the warmer parts of the ocean. The 
flat spreading species of the Frith of Forth acquire a much 
greater size than any of the branched kinds. 
The forms which this animal assumes are very various, and 
that of the spreading flat species depends much on the surface 
to which they adhere. They are found sessile, pedunculated, 
flabelliform, infundibuliform, tubular, foliaceous and branch- 
ed. From these seven general varieties of form, they have been 
divided by Lamarck into seven groups, each of which contains 
many species, again characterised by particular forms, subordi- 
nate to the general form of the group. The colours are like- 
wise employed to discriminate the species ; but as they entirely 
change by drying, they afford less useful characters. The most 
frequent colours are brown and yellow, though sponges are like- 
wise met with grey, green, and white; even red and black 
species ( Spongia rubra and Spongia nigra ) are found near 
Suez in the Red Sea. The odours of some sponges are de- 
cidedly animal, while others belong to common and well-known 
vegetables. The Spongia coalita , when newly taken from the 
water, smells very strongly of the common mussel, and when 
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 per- 
ceptible odour. 
In their natural state, they are soft and elastic, and possess 
lively colours ; but many of the species, by drying, become 
quite friable, lose their fine shades of colour, and become white. 
Soon after death, they pass through a bluish colour to black, by 
putrefaction. The whole body of a sponge is specifically hea- 
vier than sea-water ; and each of its parts taken separately sinks 
in that element. 
From the softness and permanent elasticity of the fibres of 
many species, both in the moist and dry state, this animal is em- 
ployed in the arts, and in domestic economy, where its place 
could not be supplied by any other known substance. Books 
