m 
Nature of the Spongilla friabilis. 
sponges. The pores of the lobes are nearly as large as their fecal 
orifices, and currents are as distinctl}/ seen flowing into them as 
from the latter openings. I have not been able to excite this sub- 
stance to any kind of spontaneous motion, and Blumenbach 
seems to have been as unsuccessful with those he experimented 
on at Gdttengen ; nor have I found any difference of tempera- 
ture between it and the medium in which it lives. 
The fibres forming the axis of the 8p. friabilis consist of mi- 
nute siliceous spicula, which are as regular and constant in their 
forms as the ultimate crystals of a mineral, or the spicula of 
other zoophytes, and might, like these, be employed to distin- 
guish known species, or to discover new. When we examine a 
thin layer of the recent spongilla under the microscope, we ob- 
serve the spicula placed like a frame- work round all the open- 
ings, in the order best calculated to prevent these passages from 
changing their dimensions. By agitating a portion of dt in wa- 
ter they fall asunder, and may be procured separate from the 
soft parts, but not in so pure a state as when they are obtained 
through the medium of acids. On allowing a portion of spon- 
gilla to remain for a short time in a watch-glass with nitric, sul- 
phuric, or muriatic acid, the animal matter dissolves, and the si- 
liceous spicula cover the bottom of the glass like minute shining 
crystals. They may now be washed, and their symmetrical forms 
examined under the microscope ; or they may be dried between 
plates of glass, or thin scales of mica, and thus preserved for ex- 
amination or comparison at any future period. In this species, 
the spicula have all the same form, and are mostly of one size. 
From this circumstance, and from the well-marked characters of 
the Sp. friabilis, and its abundance in most inland countries, its 
spicula may be adopted as a convenient and fixed standard of 
comparison for the description and measurement of the spicula 
of every other zoophyte. 
They are transparent, colourless, cylindrical, very slightly and 
regularly curved, pointed at both ends, tubular, hard, and brit- 
tle. They scratch glass, suffer no change in nitric acid, become 
inflated like a bottle, and burst by the sudden action of the blow- 
pipe ; do not alter their forms in the least by drying, and do not 
consume by heat. In their moist state they have a shining, vi- 
treous lustre, and appear through the microscope as if solid and 
