J. W. H. Harrison 79 



the hybridisation of such diverse strains. Incidentally, in expressing 

 this opinion, he refers to the Hagedoorns' work, and makes the definite 

 assertion that one must not assume that their novelties would always be 

 generated by crossing animals of the same racial composition. Had the 

 observed results been confined solely to the Hagedoorns' experiments in 

 America, such a criticism perhaps would have been completely justified, 

 but when we recognise that the same types of animals were obtained 

 quite independently by Bonhote in England, in hybrids of like com- 

 position, the conclusion is irresistible that the same disturbing cause 

 has sufficed in two perfectly distinct instances to produce the same 

 effect. 



Combined with mine, the evidence yielded by all these crosses tends 

 to demonstrate that in interspecific and interracial hybrids novel forms, 

 differing it is true in degree, but nevertheless quite new, are liable to 

 develop. Moreover, judging from their unusual nature, they are not the 

 products of ordinary gametic segregation and recombination; their exact 

 origin therefore remains to be discovered. 



Most geneticists, although not assenting in toto to Morgan's state- 

 ment that now "the problem of heredity has been solved "^ seem in 

 substantial agreement that it is the chromosome complex upon which 

 the actual mechanism of heredity and development depends. Admitting 

 the validity of this view, it appears certain that should any alteration 

 take place in the normal chromosomal distribution, either by the irregular 

 removal or displacement of the part or whole of any chromosome or 

 chromosomes, such a dislocation must tend to the origination of organisms 

 of an aberrant type. And, fortunately enough, cytological investigation 

 has revealed the presence of such abnormalities of chromosome behaviour 

 in the gametogenesis of interspecific and interracial hybrids. In particular 

 they have repeatedly been detected by Federley, Doncaster, and myself 

 in hybrid Lepidoptera, 



Amongst the insects in which I have observed the occurrence'* are 

 the very Tephrosias we are discussing. In the gametogenesis of their 

 hybrids many vagaries in behaviour are encountered ; often enough, in 

 the normal pairing of the chromosomes in preparation for the matura- 

 tion divisions, many chromosomes fail to find mates, so that in the 

 subsequent separation, although the individual members of those paired 

 correctly proceed as usual to the opposite poles of the spindle, in other 



1 I.e. by granting that the material basis of heredity is located in the chromosomes. 



2 The finest examples I have seen of such mitotic dislocations were in certain hybrids 

 of the genas Rosa. 



