Scientific Intelligence . — Zoology. 185 
few known species of fresh-water sponge ; but the form of one 
spiculum only, in the marine species, is of no value in character- 
ising them, from the important circumstance of the same form 
not unfrequently occurring in different species. Thus the tri-ra- 
diate spiculum of the Spongia compressor will not suffice alone 
to distinguish that species from the Spongia botryoides , since 
Ellis, Gmelin, Montagu, and Lamouroux, have described and 
delineated the same form of spiculum as occurring in the latter 
species ; but when we combine the compound tri-radiate spicu- 
lum of the Spongia compressa along with its only other simple, 
clavate, bent spiculum, we establish a scientific and permanent 
character, which will distinguish it from every existing species. 
These views, regarding the marine spicula, I had occasion, last 
winter, to illustrate in the Wernerian Society, and have since 
had an opportunity of extending them only to one species of the 
fresh-water sponge. Should the anomalous circumstance occur, 
of the same curved simple spiculum appearing in different spe- 
cies of spongilla, uncombined with any other form of spiculum, 
a specific difference must be sought for in the next character, 
pointed out by Mr Ellis in the Spongia urens , in the mode of 
arrangement of the spicula in the groups ; and this character in 
the Spongilla friabilis consists in a remarkable parallelism of 
the spicula composing all the longitudinal fasciculi. The spi- 
cula of this animal are about half a line in length, and so slen- 
der as to be almost invisible to the naked eye ; they have a shin- 
ing vitreous lustre, and appear like the finest filaments of grey 
flexible asbestus ; they do not appear to grow after they are once 
formed ; for, when the ovum has newly fixed itself, and begun 
to spread on a watch-glass, I have constantly observed, that the 
spicula make their appearance in the transparent film of their 
full size, and with their symmetry complete ; their lustre is not 
tarnished by remaining in nitric or muriatic acids ; although the 
ovum is nourished only with rain-water, it continues to secrete 
these shut, flexible, siliceous tubes. — Dr Grant. 
37. Sounds produced under water by the Tritonia arbor es- 
cens. — About a month ago I happened to place together, in a 
crystal jar filled with sea- water, some small species of Doris , 
specimens of the minute Tritonia corona ta, Eolis peregrina , and 
two of the Tritonia arbor escens, and my attention was soon af» 
