40 



just described, it is requisite to use a yet higher magnifying 

 power of the compound microscope, and choosing a small 

 transparent example to focus right down into the inner 

 substance of the living sponge. This inner substance is 

 then found to be excavated in every direction into sub- 

 spherical chambers, the walls of which are closely lined 

 with minute ovate bodies or cells. Each of these cells 

 bears at its free extremity a long whip-like appendage or 

 "flagellum," the base of which is surrounded by a very 

 delicate funnel-shaped extension of the cell substance, 

 known as the collar. Minute canals place these flagellated 

 chambers in communication with the incurrent apertures or 

 " pores " of the sponge system, while others leading from 

 the same chambers, freely anastomosing with one another, 

 and thus gradually enlarging their dimensions, finally de- 

 bouch upon the relatively large excurrent apertures or 

 " oscula." It is the incessant vibratile or lashing action in 

 one direction of the whip-like appendages, or flagella of the 

 cells lining the internal chambers of the sponge, that pro- 

 duce the inflowing and outflowing currents first observed. 

 These flagellated cells absorb and assimilate the food 

 particles brought into the sponge system by the currents 

 they collectively create, and constitute the essential living 

 elements of all sponge structures. 



It is interesting to find that among the lowest micro- 

 scopic forms of animal life, known as the Flagellate Infu- 

 soria, organisms exist, having an equivalent structural value 

 only of simple cells that possess, in a like manner, a whip- 

 like flagellum and basal cellar, and are in all other respects 

 structurally identical with these animal elements of the 

 sponge body. Some of these flagellate infusoria or 

 " Collared Monads," as they are more commonly desig- 

 nated, are solitary, while others form social colonies, which 



