Mr. H. J. Carter on the Freshwater Sponges of Bombay. 95 
expelled reaches ; although from my “ Notes” it should appear 
that it went farther, for I have therein stated, that I had seen 
the semi-transparent mucilage take on an arrangement m form 
and disposition like that of the spicula in the skeleton ; but this 
was an illusion, for I afterwards found out that this appearance 
had arisen from the semi-transparent mucilage having attached 
itself to a series of minute scratches on the surface of the watch- 
lass. 
My impression however is, that both the horny skeleton and 
its spicula are formed in the intercellular substance, and not 
within the cells. 
The spicula are membranous, and at an early period of their 
development pliable ; they afterwards become firm and brittle. If 
they be exposed to the flame of a blowpipe, many of them swell 
out towards the middle or one end into a bulb, like that of a 
thermometer. This is more particularly the case with spicula of 
friabilis than with those of any of the other species. They are 
hollow, and the form of their cavity corresponds with that of 
their own form, being widest in the centre and narrow towards 
each extremity. Sometimes they contain a green matter like the 
endochrome of cells of Confervee. 
Growth.—This only takes place during the time Spongilla is 
covered by water, which in the tanks of Bombay is not more than 
eight, or at the farthest nine nionths out of the year, but the 
duration of its submergence of course again varies with the posi- 
tion it occupies on the sides of the tank. Its mcrease however 
appears to be most rapid in September and October, 2. e. about 
two months after the tanks have become filled ; subsequently it 
appears to go on more slowly. During the season of its growth, 
or while it is under water, it may extend from a portion, not 
more than a few lines in diameter, over a surface 2 or 3 feet in 
circumference, or it may evince no disposition whatever to ad- 
vance beyond its original bulk throughout the whole season. It 
increases in size by successive additions to its exterior. To what- 
ever extent this increase may reach, either vertically or hori- 
zontally, during the first season (assuming that it commenced 
from a central point or germ), but few seed-like bodies are deve- 
loped in it, and these few, as I have before said, are found in the 
centre or first-formed portion. The next year the development 
of its fleshy substance appears to commence from these seed-like 
bodies, which a few weeks after it has again become submerged, 
pour forth their contents over the last year’s skeleton, and reach- 
ing its circumference develope a new portion ; and in this way, 
by successive additions, it gradually increases m bulk, while the 
seed-like bodies accumulate about its centre, till at length it ke- 
