GERMINAL SELECTION 457 



occurrence in development, where we often see one organ 

 waxing and another waning, we must regard it as part of the 

 plan of campaign which is hereditarily predetermined in the 

 germ-plasm. But since the organism develops in intimate 

 dependence on a changeful environment, we are prepared for 

 local modifications of adjustment arising as the results of histonal 

 selection. Many malformations represent attempts on the 

 organism's part to solve an insoluble problem forced upon it by 

 peculiar environmental conditions ; many individual adapta- 

 tions are wrought out by the modus operandi of histonal selection 

 in the individual lifetime, and are of real value to the organism 

 that acquires them. But there is no good reason for believing 

 that either can be entailed on the offspring. 



None the less, it is important that the student of inheritance 

 should vividly realise the existence of this modus operandi 

 which Roux called the "struggle of parts within the organism." 

 For, although we cannot say that it has any direct evolutionary 

 importance in securing new steps in evolution, and although we 

 do not understand how it is that parts regulate themselves 

 appropriately in reference to new conditions of stimulus — for 

 that is obviously part of the secret of life itself — it is useful 

 to bear in mind that there is in a real sense a competition among 

 organs, a struggle of parts, and a warfare among cells. Vivid 

 illustrations may be found in the histolysis or disruption of 

 tissue associated with metamorphosis (e.g. in many insects), 

 in the behaviour of teratogenic growths, in the involutions or 

 degenerations associated with senility (e.g. in the invasion of 

 the brain of the aged parrot by hungry " neurophagous " cells) , 

 and in the familiar fact that the hypertrophy of one organ may 

 handicap or even suppress another organ. 



In short, the concepts of struggle and selection may be ex- 

 tended to the parts of the organism. 



Struggle between Gametes. — There may be struggle be 

 tween groups of organisms, struggle between individual organ- 



