352 THE BIOLOGY OF INSECTS 



plasm must continually occur, and there is little doubt 

 that these are modifications of chemical constitution and 

 shifting of the position of particles in the chromosomes. It 

 is evident also that if these changes in the germ-plasm 

 become apparent in the characters of the organism that is 

 developed from the egg, there must be some arrangement 

 for passing on to the cell-substance the effect induced by 

 the germinal modification. ** That which is conferred in 

 variation," suggests W. Bateson (19 14), '* must rather 

 itself be a change not of material but of arrangement or of 

 motion." It is well known to students of inheritance on 

 Mendelian lines that factors for apparently new characters 

 may become apparent through the ** release " of factors in 

 the germ-plasm, owing to the elimination of other germinal 

 factors which act as inhibitors. This mode of germinal 

 working has led Bateson to the conclusion that '' variation 

 both by loss of factors and by fractionation of factors is a 

 genuine phenomenon of contemporary nature," and from 

 this starting-point to suggest that " we must begin seriously 

 to consider whether the course of evolution can at all reason- 

 ably be represented as an unpacking of an original complex 

 which contained within itself the whole range of diversity 

 which living things present." With regard to the moth 

 Amphidasys betularia, mentioned above, Bateson com- 

 ments : " Though at first sight it seems that the black must 

 have been something added, we can without absurdity 

 suggest that the normal is the term in which two doses of 

 inhibitor are present and that in the absence of one of them 

 the black appears." From many points of view such a 

 speculation is fascinating and alluring ; it is not easy, 

 however, to accept the conclusion that increasing com- 

 plexity of structure and perfection of behaviour in the 

 developed creature has been brought about not through 

 elaboration but through progressive simplification of the 

 germ-plasm. We should indeed regard with wonder the 

 primitive thysanuriform insects of the early Palaeozoic 

 periods, if we could believe that in their germ-cells, veiled 

 as yet by numberless inhibitors, there were lying latent 



