154 VIGNETTES FROM INVISIBLE LIFE. 



The Sponge is wonderfully tenacious of life, 

 and will undergo propagation by cuttings ; or it 

 will multiply itself voluntarily by the analogous 

 process of self-division, or, reversing this process, 

 it multiplies the Spongy bulk by diminishing the 

 number of individuals, by a process of fusion or 

 amalgamation with its neighbours, so completely 

 joining with each other as to leave no line of 

 demarcation to tell the curious tale. In this way 

 it becomes encrusted in large masses on floating 

 timber and the sides of docks and canals, or in 

 large globular clusters in slowly moving streams, 

 sometimes of a bright green colour, or in irregular- 

 shaped bodies of a whitish appearance, attached 

 to the stems and leaves of plants. The peculiar 

 irregularity of this last form forcibly reminds one 

 of the chalk flints, and when it is remembered that 

 these are fossil marine Sponges the coincidence is 

 interesting as incidentally furnishing evidence of 

 common origin. 



One cannot speak of Sponges without at the 

 same time speaking of spicula. Yet the spiculum 

 is not an essential adjunct of Sponge life, as we 

 all know by daily experience of the toilet Sponge, 



