PROPAGATION OP SPONGES. 387 



detected but in one genus of full-grown marine sponges) a 

 constant circulation is kept up, providing the sponge with 

 nourishing particles and oxygen, and enabling its system ot 

 channels to perform the functions both of an alimentary tube 

 and a respiratory apparatus. 



Dr. Grant describes in glowing terms his first discovery of 

 this highly interesting phenomenon: "Having put a small 

 branch of sponge with some sea-water into a watch-glass, in 

 order to examine it with the microscope, and bringing one 

 of the apertures on the side of the sponge fully into view, 

 I beheld for the first time the spectacle of this living fountain, 

 vomiting forth from a circular cavity an impetuous torrent 

 of liquid matter, and hurling along in rapid succession opaque 

 masses, which it strewed everywhere around. The beauty 

 and novelty of such a scene in the animal kingdom long 

 arrested my attention, but after twenty-five minutes of con- 

 stant observation, I was obliged to withdraw my eye from 

 fatigue, without having seen the torrent for one instant change 

 its direction or diminish in the slightest degree the rapidity of 

 its course. I continued to watch the same orifice at short 

 intervals for five hours, sometimes observing it for a quarter of 

 an hour at a time, but still the stream rolled on with a constant 

 and equal velocity." 



Subsequent observations have proved that the living sponge 

 has the power of opening and closing at pleasure its oscula, 

 which are capable of acting independently of each other, thus 

 fully establishing the animal nature of these simple organisations, 

 in whom latterly even traces of sensibility have been detected, 

 such as one would hardly expect to meet with in a sponge. For 

 these creatures, as we are entitled to call them, are able to 

 protrude from their oscula the gelatinous membrane which 

 clothes their channels, and on touching these protruded parts 

 with a needle, they were seen by Mr. Grosse to shrink imme- 

 diately — a proof that the sponge, however low it may rank 

 in the animal world, is yet far from being so totally inert or 

 lifeless as was formerly imagined. 



The propagation of the sponges is provided for in a no less 

 wonderful manner than their respiration and nourishment. 

 Minute globular particles of sarcode sprout forth as little pro- 

 tuberances from the interior of the canals. As they increase in 



