100 MARINE BIOLOGICAL LABORATORY. 



less similar cells, that those individuals which were laden 

 with food matter should not remain at the periphery, 

 but should pass to the centre, not only to equalize the 

 weight of the various parts of the colony, and to allow 

 the more active cells free action at the periphery, but 

 also to permit these food-laden cells to carry on their 

 assimilative functions without disturbance from external 

 conditions. 



*' For a long time the individuals of any colony prob- 

 ably differed only quantitatively ; the locomotor cells 

 attracted food particles by the movement of their fla- 

 gella and also absorbed some of the smaller particles, just 

 as the ectoderm cells in some Coelenterates of to-day 

 occasionally ingest food-matter. The inner amoeboid 

 cells, however, were on the other hand capable of swal- 

 lowing larger food particles. Probably when so engaged 

 the amoeboid cells approached the periphery, and gained 

 possession of food particles lying on the surface of 

 the colony by means of the numerous pores between 

 the cells of the superficial layer. . . . Gradually the 

 differentiation in this direction progressed ; the loco- 

 motor cells lost more and more their food-ingesting 

 function, which concentrated itself in the amoeboid 

 phagocytes; the occasional fine pores between the loco- 

 motor cells enlarged and became openings similar to 

 those so numerous on the surface of a sponge. . . . 

 With the increased activity of the Metazoa, now pro- 

 vided with two primitive organs, there must also have 

 been an increased necessity for food, and larger plant 

 and animal organisms must have served as prey. To 

 make this possible one or more larger openings arose, 

 which led to the formation of a mouth." 



