332 THE AMERICAN MONTHLY [Dec 



ception of their structure before we can eater, with intel- 

 ligence, into the everyday-life of such a sponge as we are 

 now considering. They are exceedingly minute in size, so 

 small that from 5,000 to 10,000 of them placed close to- 

 gether side by side would only form a line one inch in 

 length, and yet so wonderfully formed as to be able not 

 only to capture the food particles, but also to digest the 

 same in a manner analogous to the digestive cells of ani- 

 mals infinitely removed from them in the animal king- 

 dom. Typically, a collared cell cousists of a rounded or 

 sometimes cylindrical body produced above into a neck. 

 The neck is surmounted by a comparatively long vibratile 

 whip-like flagellum which is surrounded by a very deli- 

 cate transparent membranous collar which is usually more 

 or less funnel-shaped and inserted in the neck around the 

 flagellum. In the body of the cell is a specialized part of 

 the protoplasm, which shows a great affinity for the stain- 

 ing material used in the preparation of the section, known 

 as the nucleus, and lying near to it are one or two open 

 spaces called contractile vacuoles. As far as I know, 

 these collared cells have never been seen in the act of 

 feeding in the sponge itself, but there is an animal (Mon- 

 osiga gracilis) belonging to the great division of the ani- 

 mal kingdom known as Protozoa or one-celled animals, 

 which is almost identical in structure to the collared cell 

 of the sponge, and the feeding habits of this form have 

 been very carefully observed. When in action, the flagel- 

 lum projects freely through and beyond the cavity of the 

 funnel-shaped collar, and being in constant movement to 

 and fro with a swinging motion causes a current of water 

 whose general direction is towards the collar. By means 

 of this current the animal secures its food. All sorts of 

 minute particles are carried against the collar. These 

 particles, however, do not remain stationary in the spot 

 where they come into contact but are carried irresistibly 

 up the outside of the funnel to the edge of the opening, 



