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 in 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- 

 glass. 



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 Confervse. 



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 months 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 increase however 

 appears to be most rapid in September and October, i. 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 in bulk, while the 

 seed-like bodies accumulate about its centre, till at length it be- 



