46 J. G. WALLER ON FRESH-WATER SPONGES. 



traction, and the density of the organism ; the projecting osculum 

 was withdrawn, and in three weeks disappeared, leaving in its place 

 a large opening or depression, which was very variable in size and 

 appearance even on the same day. The sponge now assumed an 

 ovate character, having a smooth surface, and no projecting spicula 

 except at one end. From this it passed step by step into a globular 

 form of a deep emerald green colour ; its attachment to the capsule 

 became smaller and smaller, until at length it broke away, and 

 disappeared (Fig. 8). 



Now this was exactly the course which every other specimen fol- 

 lowed. All from an expanded membrane, covering granular matter, 

 contracted into a globular shape, then separated from its attachment, 

 and disappeared. The only difference being that colour was acquired 

 in other instances, whilst it was still expanding and growing upon 

 the old sponge, and some were larger than others. Every indivi- 

 dual, if such an expression can be correctly applied, had one 

 osculum projected from it, and on this interesting organ I will add 

 a few more remarks. Dr. Bowerbank states that this pellucid tube 

 " exists only during the course of the energetic excurrent action." 

 As far as I have observed this was not exactly the case. By re- 

 ference to Plate iii. you will perceive two conditions in the same 

 example. In Fig. 1 the sponge is active, the dermal membrane is 

 fully extended, supported, as it were, at the apices of the spicula, 

 and reminding one of a tarpauline over a hay-rick. Here the 

 osculum is firm and erect. In the passive state the membrane is 

 contracted, the osculum hangs down in a flaccid state, and the 

 sponge is evidently at rest (Fig. 2). I found if the sponge was 

 disturbed it went directly into this condition, and I fancied, upon 

 one or two occasions, a dull and heavy day produced the same 

 effect. The corrugated structure of this organ shows that the 

 power of contraction and expansion must exist to a great extent ; 

 but I never saw any absolute withdrawal of it, except under the 

 conditions mentioned. 



The phenomena, I have endeavoured to describe, seem to point 

 to an act of gemmation with which we are familiarised in many of 

 the lower orders of animal life, and which are well known to take 

 place in, probably, every sponge ; and yet these are great differences 

 from our usual experience. Here it is clearly a young sponge 

 which gradually assumes this ajDpearance. It is well, therefore, 

 to follow up the ensuing stage if possible, and happily this I am 



