184 Scientific Intelligence. — Zoology. 
bottle in some part of its course, generally in the middle, some- 
times near one end, and bursts without any audible decrepita- 
tion. In their white, opaque, calcined state, nitric acid, vinegar, 
or muriatic acid, produce no more effect on them than pure wa- 
ter. It is stated by Lamouroux that the burnt ashes of the 
spongilla abound so much with lime, that sometimes more than 
half of their weight is composed of that earth * ; he has not men- 
tioned, however, the species in which he met with this appear- 
ance, and may possibly have been deceived by portions of shells 
in its substance, or by small fragments of the calcareous rocks 
on which the animal grew. When the spicula are examined 
through the microscope after this exposure to heat, we distinctly 
perceive a shut cavity within them, extending from the one point 
to the other ; and on the inflated part of each spiculum we ob- 
serve a ragged opening, as if a portion had been driven out by 
the expansion of some contained fluid. In those spicula which 
had suffered little change of form by their incandescence, I have 
never failed to observe the same cavity within, extending from 
one end to the other, and a distinct open rent on their side, by 
which the contained matter has escaped before the usual globu- 
lar distension had taken place. From the constancy of the form 
of this spiculum, in every variety of Spongilla friabilis I have 
met with in Lochend, whether lobed, branched, flat, or globu- 
lar, grey coloured, or green, young, or old, I am convinced that 
it will afford an equally useful and scientific character for the 
discrimination of this animal, as that afforded by the spicula of 
the marine sponge, and ought, in like manner, to have a place 
in the definition of the species. This interesting character in the 
marine sponges has been neglected by Lamarck, and only par- 
tially adopted by Donati, Ellis, Gmelin, Montagu and Lamou- 
roux. Although the spiculum above described occurs uncom- 
bined with any other form in this fresh-water species, and pos- 
sesses nearly the simplest possible form, we almost always ob- 
serve in the marine sponges a combination of more than one pri- 
mitive form in the same individual ; and these forms often very 
complicated, as in the tri-radiate and quadri-radiate spicula. The 
form of a single spiculum may be sufficient to distinguish the 
Hist, des Polyp. 1816, a-Ephydatia. 
