98 ANIMAL INDIVIDUALITY [CH. 



So far the analysis of the simple sponge individual 

 has shown it to be composed of definite, separate 

 cells. These in the normal animal have considerable 

 freedom and independence, both structurally and 

 functionally. Under the artificial conditions of ex- 

 periment, this independence is shown to be very 

 large, inasmuch as one kind of cell at least can live 

 alone, leading a strange new life, when separated 

 from the rest of the body. Though the whole sponge 

 is a true individual, composed of harmonious parts, 

 yet those parts can themselves behave as harmonious 

 wholes. So far, their independence is merely stated 

 and proved ; by their history it can be more or less 

 explained, for various converging testimonies all 

 point to one conclusion, that Sponges are descended 

 from a particular group of Protozoa, and that there- 

 fore every cell now forming part of a sponge's body 

 is derived by an unbroken chain of cell-division 

 (interspersed of course throughout with sexual cell- 

 fusion) from cells which existed as free-living and 

 independent individuals. 



On the other hand there does exist a sponge- 

 individuality higher than that of the cells : to start 

 with, in the normal sponge all these cells are working 

 together for a common end, so that every part helps 

 every other part ; and in the second place, the plan 

 of this higher individuality somehow permeates all 

 the cells, so that from any group of all the kinds of 



