THEORIES AND PROBLEMS OF CANCER 675 



tion and multiplication into groups will take place. I have called 

 this form of co-ordination " somatic " x and the phenomenon seems 

 readily explicable as the result of natural selection upon varia- 

 tions. Variations occur in all directions and only where variation 

 towards interdependence occurred in contiguous unicellular 

 organisms could multicellular organisms have been produced. 

 There is abundant evidence to prove that the general poten- 

 tiality shown by the separated blastomeres is retained to a 

 certain extent by the cells forming the bodies of adult animals, 

 though it becomes less as the later stages of evolution are 

 reached and is probably at the minimum in mammals. 



It is quite clear that if a portion of the body of an animal be 

 removed, the cells of that part cease to be in somatic or any 

 other kind of co-ordination with the body from which it is 

 separated. There is, however, a process which is perfectly 

 normal and part of the healthy life history of every multi- 

 cellular organism by which some of the cells pass out of somatic 

 co-ordination. 



We have seen that a new multicellular individual is produced 

 by the fusion of two cells derived from two pre-existing indi- 

 viduals of the same kind, the parent organisms. These cells 

 which are separated from the body of the multicellular organism 

 are known as " gametes " — the ova or eggs in the female, the 

 sperms in the male. It is quite evident that the gametes them- 

 selves pass out of somatic co-ordination, as they separate from 

 the body in which they arise ; but it is also certain that the cell 

 ancestors of the gametes are out of somatic co-ordination during 

 many generations with the body which produces them. That 

 these cells are in fact practically independent organisms living 

 in a parasitic manner upon the parent body is very obvious in 

 certain plants in which the gametogenic cells (those from which 

 gametes will be produced after a number of cell generations) 

 actually destroy and live upon adjacent cells. We have then 

 the established fact that certain cells derived from the bodies 

 of plants and animals, including man, pass out of somatic 

 co-ordination by a purely physiological (normal and healthy) 

 process, though they remain attached to or contained within the 

 body for some time, living upon it in a parasitic manner. 



1 Walker, Charles, Esse?itials of Cytology, Constable, London, 1907, and else- 

 where. Soma is the term generally applied to the body of the multicellular 

 organism, excluding the reproductive cells. 



