396 LOTSY, CURRENT THEORIES OF EVOLUTION. 
in a sense akin to that of DE Vries, if the two chromosomes in 
question possessed identical structure. . 
Taking up the historical thread again, we must now ask how it 
happened, that DE VRIES’ deductions from his Oenothera-observations 
were so readily accepted, notwithstanding the fact, that he himself 
stated not to have caused O. Lamarckiana to mutate but merely 
to ‘have observed the throwing of aberrant forms by it. 
It seems to me that the reason of this ready acceptance, was the 
great relief we all felt, that that elusive damsel transmittable varia- 
bility, in whose existence we all believed, seemed finally to have 
been entrapped. 
And even, at the present moment, the belief in the existence of 
dame transmittable variability, is so great, that she is still diligently 
pursued. 
I shall not refer to all cases of supposed mutation found in the 
literature, nor could I, where the time at my disposal is so short 
for so vast a subject as I was asked to present to you, but shall 
limit my remarks to that most ingeniously worked out organism 
Drosophila ampelophila. Nor shall I discuss here the question of 
crossing over, so intimately connected with MORGAN’s acceptance 
of mutation, but only call your attention to the, it seems to me, 
significant fact, that all so called mutants obtained by MorGAN, 
except one, were obtained from wild stock. 
In other words: all forms obtained by him from the wild stock, 
except one, proved to be constant in regard to the particular 
character in which they differed from the wild stock. 
From this, to me, the most logical conclusion seems to be, that 
the wild stock which throws the supposed mutants is impure, 
and that, after purification, the phenomenon of mutation ceases. 
It is true, that sometimes a deviating form appeared among the 
mutants, but of these MORGAN himself says: 
„It would bea point of capital importance, if it could He determined 
beyond doubt that at times recessive mutant genes change back 
to the original (wild type) gene, or even if a recessive gene could 
mutate to a dominant one. The appearance of the wild type in a 
pure culture of a mutant race can be accepted as good evidence 
of such a change only, when every possibility of contamination by 
the wild type is excluded and this is difficult to regulate. In our 
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