35 



allowing any factor for colour in the germ-plasm to make itself 

 evident in the animal, and the " albino " constitution prohibiting 

 such manifestation, although not destroying the determining factors 

 for colour. By the help of this conception Cuenot has not only been 

 able to reduce the previously existing chaos of experimental results 

 with regard to the colour of mice to order, but has been able to 

 anticipate correctly the results of complicated matings not previously 

 carried out. He made a similar assumption with regard to the distri- 

 bution of the coat-colour, whether uniform or " panachee," and found 

 that the facts could be explained by Mendel's law in this way. 

 Exactly comparable results have been obtained by Hurst with rabbits 

 for both coat-colour and coat-pattern. 



Whilst, therefore, Mendel's law appears to be of even wider appli- 

 cation than at first supposed, it is only fair to state that a certain 

 number of facts have come to light which cannot be made to 

 harmonise with the conception of gametic purity, at least in its 

 original simple form. One example must suffice. In studying 

 the hereditary peculiarities of the comb in fowls Bateson and 

 Punnett found that "rose" and "pea" combs both behaved as 

 simple dominants to the " single " comb, but that when they were 

 crossed they gave rise to a comb practically the same as the. "walnut" 

 comb of Malays. These fowls with " artificial " walnut combs, when 

 bred together, and also when crossed with those having single combs, 

 produced progeny exhibiting all four types of comb, to account for 

 which it is necessary to assume that the compound factor for the 

 walnut comb had been broken up not only into the rose and pea 

 factors but into the single-comb factor as well. Needless to say, this 

 conception of compound allelomorphs, as they have been called by 

 Bateson, acting, according to circumstances, sometimes as single and 

 sometimes as multiple factors, is an extremely important extension of 

 the original idea of unit characters. There appears, however, to be 

 a good deal to be said in favour of the acceptance of such a notion as 

 a legitimate development of Mendel's law.* 



Just one other point must be referred to in connection with the 

 recent work inspired by the unearthing of Mendel's paper, and that 

 is the attempt which is being made to explain the postulate of 

 gametic purity in terms of cell-division phenomena. It is evident 

 that if the cytological evidence were distinctly incompatible with the 

 idea of gametic purity Mendel's law would have to be reconsidered. 

 This, however, is not the case. On the contrary, there are many 

 phenomena connected with the processes of the maturation of the 

 germ-cells and fertilisation which seem to justify views regarding the 

 bearers of the hereditary tendencies (chromosomes) which are com- 



* A supposed simpler explanation of the particular case mentioned, based on 

 the assumption that two pairs of characters are involved in the " rose " and 

 " pea" combs, has been put forward in a later paper by Bateson and Punnett. 

 There remain other cases, however, which seem to require the conception of 

 compound allelomorphs for their explanation. 



