420 "S. J. Holmes 



The process might be illustrated by the case of a social organism 

 composed of animal cells and symbiotic algse which I described in 

 my former paper. "We may suppose that both animal and plant 

 cells tend to grow and multiply as far as circumstances permit. 

 As these cells depend upon each other to a certain extent, neither 

 kind of cell will tend to preponderate over the other, but they will 

 all adjust themselves to a condition of approximate equilibrium. 

 Now suppose that a considerable number of the algae of this com- 

 posite organism be removed. There is a functional demand by 

 the rest of the organism for the products of the algae and an excess 

 food supply for those which remain. The algae, therefore, are 

 supplied with exceptionally favorable conditions for growth and 

 multiplication, and will be stimulated to regenerate their missing 

 number. By supplying the functional demand of the animal cells 

 they indirectly benefit themselves, because by producing more 

 oxygen they enable the animal cells to produce more of the sub- 

 stances which they utilize as food. If we suppose that in our 

 hypothetical organism there are, in addition to the two kinds of 

 cell mentioned, indifferent cells which are able to develop into 

 either animal cells or algae, it seems probable that, in the event ol 

 the removal of the algae, the indifferent cells will differentiate so 

 as to take the place of the missmg numbers. * * * 



"For the sake of a simple illustration we have described an 

 organism consisting of but two kinds of cells, but there is no reason 

 to doubt that in a complex organism consisting of many varieties 

 of cells standing in a symbiotic relation there would be a similar 

 regeneration of any part that is removed. Let us imagine an or- 

 ganism made up of a number of differentiated cells, each of which 

 derives some advantage from some substances produced by the 

 contiguous cells, and giving out some substance upon which the 

 contiguous cells are more or less dependent. We will suppose 

 that, in addition to these differentiated cells, there are scattered 

 through the body numerous indifferent or embryonic cells whose 

 multiplication is held in check by the others, but which upon the 

 removal of any part respond to the functional disturbance by 

 growth and multiplication near the place of mutilation. We may 

 represent our hypothetical organism graphically bv the following 



