3502 



THE SPONGES 



holes at the summits of the craters are termed oscules, and the small ones on 

 the general surface, pores. Ellis, who put some specimens in a glass vessel of 

 sea water, wrote that ' ' We could plainly observe these little tubes to receive and 

 pass the water to and fro;" and further, "The sponge is an animal whose 

 mouths are so many holes or ends of branched tubes opening on its 

 surface; with these it receives its nourishment, and by these it discharges like 

 the polyps its excrement. " Ellis' s observations were erroneous in one important 



point. The water always passes 

 out of the large orifices, and is 

 not passed in by them. It is 

 true that while the torrent is 

 gushing out of the centre of an 

 oscule, there is a slight pas- 

 sive return current at the mar- 

 gin. Ellis attributed the cur- 

 rent to the contraction of the 

 walls of the canals. He found 

 that the current continued in 

 the absence of any worms or 

 crustaceans in the body of the 

 sponges. 



Our knowledge of sponges 

 really begins in 1825 with the 

 observations of Grant, who ex- 

 amined a fragment of a living 

 branch of a branching sponge. 

 On bringing one of the large 

 apertures on the side of the 

 branch fully into view, he 

 beheld this living fountain 

 vomiting forth from a circular 



a. FI.AGEU.ATED CHAMBER OF 



BREAD-CRUMB SPONGE, 

 SHOWING COLLAR CELLS J b. FLAGELLATED CHAM- 



cavity a torrent of liquid matter, 



BER OF FRESH-WATER SPONGE. (Both figures 1600 ao ^ hurling along in rapid 

 diameters. ) After Vosmaer. succession opaque masses, which 



it strewed everywhere around. 



After many experiments, Grant convinced himself that a current flowed out of all 

 the large orifices, and not into one and out of another. He also rubbed powdered 

 chalk on the surface of a bread-crumb sponge, and saw particles which clogged the 

 margins of the minute pores on the surface driven into the interior; and thereby 

 demonstrated the passage of currents into the interior through the pores. The 

 origin of the sponge fountains was now traced. In all sponges currents of water 

 pass into the body through pores, and out again by one or more ways different 

 from those by which they entered. To ascertain the cause of the currents, it is 

 necessary to examine the anatomy of the sponge. A thin skin, which can be 

 peeled off, is separated from the body by numerous minute supporting pillars. On 



