146 VIGNETTES FROM INVISIBLE LIFE. 



investment and skeletal spicula, while the more 

 active food-collecting, circulatory, and respiratory 

 functions devolve on the ciliated or flagellate 

 monads. This combination of material and forces, 

 resulting in what we denominate a Sponge, though 

 apparently so simple, is not at all easy to under- 

 stand or to explain. Let us, then, bear in mind 

 that in this combination the two forms i.e., Flagel- 

 late infusoria and Amoeba are fused or amalga- 

 mated in one essential histological element or life- 

 tissue, which must now and hereafter be regarded 

 as one combined structure or individual animal 

 body, while at the same time each form preserves 

 its own essential function and work. This com- 

 bined oneness with semi-independence is charac- 

 teristic of all complex organisms, giving rise to 

 that general law of division of labour with unity 

 of purpose so essential to the welfare of the whole 

 body. The complexity of Sponge structure and 

 function is, however, of the simplest order para- 

 doxically though it sounds consisting mainly, as 

 we have indicated, of only two primary agents, 

 which, by their united and combined operations, 

 have succeeded in producing a very interesting form 



