Xlll 



of the local climate made them less or more conspicuous 

 according as they happened to be dark in a wet climate, pale 

 in a dry one, or vice versa, the eclipsed factor being for the time 

 buried deeper than is implied in ' recessive ' as used Mendelially. 

 It is generally (always?) the case that the species exhibiting 

 this resuscitated melanism presents it as a Mendelian alternative 

 to what we regard as the normal form, which it would not do 

 were it recently acquired by selection." 



Prof. Poulton said that the chief difficulty he felt on reading 

 carefully this most interesting and suggestive note was in Dr. 

 Chapman's " belief that a factor is represented in the germplasm 

 by a differentiation in the structure ... of every molecule of 

 the plasm; that it is present in every portion of the plasm " 

 (p. x)— words that were somewhat difficult to reconcile with 

 those that immediately followed them; as also with the 

 hypothesis that " the factors for some particular character, 

 in two porfions of germplasm of two different individuals, may 

 combine freely," etc. (p. x) ; and especially with the "broad 

 view . . . that each species has a germplasm consisting of an 

 enormous number of factors " (p. xi). To suppose that every 

 one of this eno.rm-ous number was represented in every mole 

 cule of the plasm called up a vision of bewildering complexity. 



To refer to one other conclusion (p. xii) — a Mendelian 

 recessive, if present in a sufficiently small proportion of the 

 population would seem to provide a burial so deep that a 

 character might lie hidden for ages. On the other hand, 

 hidden characters, like the melanism of hetularia, were often 

 Mendelian dominants and would appear when heterozygotes 

 no less than when pure, so that here some form of deeper than 

 Mendelian burial might be a necessary hypothesis. 



As regards the suggestion that factors " acquire ininiisci- 

 bility ... by natural selection " (p. xi), he had always 

 believed that the growth of a complex mimetic pattern had 

 been along these lines— viz. at first small variations — non- 

 Mendelian ; then, as by selection these became larger and 

 larger, a point was reached when they followed the Mendelian 

 rules. This could j)robably be tested in the primitive female 

 forms of Papilio dardanus Brov/n, at Nairobi. 



