32 BY THE DEEP SEA. 



will re-appear, not where they went in, but in a denser stream 

 issuing from one of the craters, which are scientifically 

 designated oscula to distinguish them from the minute pores. 



If we dissect the sponge 

 under a microscope, we shall 

 find that from one of these 

 oscula a broad passage runs 

 through the centre of the 

 mass, and from the walls of 



SECTION THROUGH CRUMB-OF-BREAD ^^ ^ m i nu te pOrCS TUn off 





SPONGE. ., r r~, . 



to the outer surface. This 



central cavity is invested by a living membrane which, when 

 examined through a higher power of the microscope, is seen to 

 consist of myriads of organisms closely packed together side 

 by side, and each resembling a glass vase, spherical below, 

 with a wide neck, and from its centre there issues a long 

 antenna-like process. This is called the flagellum (Latin, 

 a whip), because its office is to lash the water. These flask- 

 like organs, with their flagella, present a wonderful likeness to 

 some free infusoria known as collared monads, and over this 

 likeness and all that it may or may not imply to the systematic 

 naturalist much ink has been shed, and the sounds of contro- 

 versial strife it engendered, though now faint, are still audible. 

 Into that question we do not go. 



The combined lashing of these little whips in unison sets a 

 strong current of water flowing through the central passages 

 and out at the oscula. To feed this stream, water flows in 

 automatically through all the little pores, and brings with it 

 the infusoria and other minute particles of life with which the 

 sea is swarming. These come in contact with the lips of the 

 flasks in the interior over which the living jelly of the sponge 

 is steadily flowing. The infusoria flow with it and are carried 

 away by the current to a little clear space (vacuole) in the 

 lower part of the flask, where it is digested, and the refuse 

 portions are thrust out to go in the general stream and be 



