THK PRESIDENT'S ADDRESS. 475 



hydroid colony, such as Eudendrium or Pennaria, be cut up 

 into small pieces and then squeezed through fine silk gauze, 

 it is reduced to a kind of cream or pulp in which the constituent 

 cells are more or less completely separated from one another. If 

 kept under suitable conditions, however, in pure sea-water, the 

 separate cells join together again in irregular assemblages, 

 to which Wilson has given the name " restitution masses," 

 and such a restitution mass may behave like an embryo and 

 develop into a new hydroid colony. The cells arrange themselves 

 in the proper layers, ectoderm and endoderm ; the ectoderm 

 secretes a new horny perisarc, branches grow out, and finally 

 new hydroid polyps are produced at the ends of the branches. 



It is impossible in such a case to formulate any definite 

 relations between the component individuals of the original 

 colony and those of the new colony developed from the restitution 

 mass. The whole thing was simply pulped, and the separated 

 cells apparently reduced to an indifferent condition with powers 

 of fresh association in new combinations, while many of the 

 original cells seem to be used simply as food-material for the 

 new colony. 



This experiment is to some extent paralleled by what takes 

 place normally in the development of the gemmules of the 

 freshwater sponge. A number of wandering amoebocytes, 

 charged with food-yolk, migrate to one spot in the parent 

 sponge, and there become enclosed in the characteristic capsule 

 secreted by surrounding cells. On germination the capsule is 

 ruptured, and an amoeboid mass creeps out ; the constituent 

 cells behave like the blastomeres of an ordinary embryo, multiply 

 rapidly and become differentiated into the various tissue cells, 

 which arrange themselves in the manner characteristic of 

 the adult. 



Such phenomena certainly suggest the existence of some directive 

 influence which enables the separate parts to co-operate in the 

 formation of a whole individual, but what is the nature of this 

 directive influence and where it is located are complete mysteries. 

 We have now inquired, so far as time permits, into the 

 question whether or not it is possible from the morphological 

 point of view to give any definition of individuality of general 

 applicability. We have seen that in the course of evolution 

 individuals of a lower order have given rise to individuals of a 



