THE VICTORIAN NATURALIST. 67 



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 ( Monosiga gracilis) belonging to the great 

 division of the animal 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 fiagellum 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, then over the edge 

 and down the inside till they reach the body of the animal 

 at the bottom of the funnel when they are engulphed in 

 the soft protoplasm ; the nutrient material is taken up 

 by the protoplasm, and the waste matter probably excreted 

 by means of the contractile vacuoles. 



We are now in a position to understand a few more details 

 about the canal-system of the sponge. We have already learned 

 that the water enters through minute pores in the outer layer, 

 and that, somehow or other, it finds its way through the fairly 

 thick wall into the central cavity. The wall, as we have seen, is 

 made up of the flagellate chambers together with the gelatinous 

 material and embedded spicules which form the boundary or 

 supporting structures to the chambers, and the water passes freely 

 through the wall in a very definite course. Why does it take that 

 course ? Minute examination of the wall of the flagellate chambers 

 elicits the fact that at intervals between the collared cells which 

 make up the wall small holes or prosopyles occur through which 

 water can easily pass when impelled to do so by the violent move- 

 ment of thousands of the minute vibratile processes of the collared 

 cells. This accumulated movement is the motive power of the 

 current. As the water sweeps through these tiny holes and 

 bathes the wall of the chamber studded with the cells the food 

 particles are detained by the protoplasmic collars and by them 

 transmitted to the digestive portion of the cell. The water thus 

 robbed of its nutrient material, and bearing with it the rejected 

 portions of the food particles, passes through the chamber to join 

 the general current which issues from the gastral cavity at the top 

 of the sponge. To summarize the course of the current we may 

 refer to its entry by the pores and so into minute irregular 

 channels, inhalent canals, which penetrate the gelatinous material 

 and reach the wall of the flagellate chambers ; then through small 

 holes or prosopyles in the wall of the chambers ; then through the 



