96 Mutations and Evolution. 



by the F 5 generation it is fully developed. This is said to be 

 accompanied by an increase in the musculature of the arms. The 

 development and regeneration of the pad are found to be independent 

 of hormones from the sex organs, since castration of the males 

 does not affect it. Also it is said that when F 2 males in which the 

 patch had partly developed were crossed with normal Alytes females 

 without a patch, a Mendelian result was obtained. This will 

 certainly require additional evidence before it can be accepted. 



The fact that in all Anura this pad only becomes apparent 

 during the breeding season, seems to indicate that it is of relatively 

 recent origin and has not become fully established in the germplasm. 

 It is still in the condition of an organismal rather than a nuclear 

 character. Whatever interpretation is put upon these results, as 

 indicating a return to ancestral conditions or otherwise, it seems 

 difficult to escape the conclusion that functional inheritance has 

 taken place in these experiments 1 , even if the gradual transition be 

 looked upon as a reversion. Nevertheless, one can scarcely suppose 

 that evolutionary adaptation takes place at any such rapid rate. 



It is at any rate an advantage that the subject of inheritance of 

 acquired characters is emerging from neglect into the region of critical 

 experiment, and the attitude with regard to it is becoming less 

 dogmatic and more cautious. Darwin found no difficulty in 

 accepting both the Lamarckian and selection factors as contributory 

 to evolution. We are endeavouring to show that from the point of 

 view of our present knowledge of organic structure the neo- 

 Lamarckian and mutation factors are not incompatible or mutually 

 exclusive. 



A recent paper which is ot interest because it frankly subsumes 

 the neo-Lamarckian factor (Roberts, 1919), developes the hypothesis 

 that mechanical reaction to stress is the law in all tissues. Just as 

 the flying buttresses of a Gothic cathedral were the result of an 

 effort to shore up walls which were spreading under the increased 



1 MacHride (1919) upholds Hammerer's contention. Bateson (1919) in a 

 reply points out that the fingers in the photograph of the control frog in 

 Hammerer's paper have been clumsily retouched or painted over, and that the 

 critical photograph showing the Brunftschwielen of the modified male shows 

 what appears to be a sort of excrescence on the outside of the fourth 

 finger of the right hand. This, however, does not alter the evidence for the 

 presence of a Rrunftschwiele, which is clearly shown in the photograph as a 

 lump on the right wrist. Moreover, a series of nine histologicai drawings from 

 sections of the horny pad are given, showing the details of structure of this 

 region in males of Alytes in which it is wholly or partly developed, also during 

 the breeding and resting seasons, and in females. These drawings must 

 either be regarded as evidence, in which case they prove Hammerer's point, or 

 treated as deliberate frauds. There seems no sufficient reason for adopting 

 the latter alternative, but it is certainly to be expected that Dr. Hammerer 

 will now be able to produce specimens showing the horny pad. 



