INTERSPECIFIC STERILITY 79 



1 [Jan.] 10, [186,-..] 

 ' In plants the test of first cross seems as fair as test of 

 sterility of hybrids. And this latter test applies, I will 

 maintain to the death, to the crossing of varieties of 

 Verbascum, and varieties, selected varieties, of Zea. You 

 will say Go to the Devil and hold your tongue. No, 

 I will not hold my tongue ; for I must add that after 

 going, for my present book [ Variation under Domestica- 

 tiou\ all through domestic animals, I have come to the 

 conclusion that there are almost certainly several cases of 

 two or three or more species blended together and now 

 perfectly fertile together. Hence I conclude that there 

 must be something in domestication, — perhaps the less 

 stable conditions, the very cause which induces so much 

 variability, — which eliminates the natural sterility of 

 species when crossed. If so, we can see how unlikely 

 that sterility should arise between domestic races. Now 

 I will hold my tongue.' x 



Darwin made attempts to ' produce physiological 

 species by selection ', and thus meet his friend's criticism. 

 He thought out and suggested a plan of experiment 

 to W. B. Tegetmeier, 2 and gave a brief account of the 

 scheme to Huxley, December 28, [1862] : — ' I have . . . 

 given him [Tegetmeier] the result of my crosses of the 

 birds which he proposes to try, and have told him how 

 alone I think the experiment could be tried with the 

 faintest hope of success — namely, to get, if possible, 

 a case of two birds which when paired were unproductive, 

 yet neither impotent. For instance, I had this morning 

 a letter with a case of a Hereford heifer, which seemed 

 to be, after repeated trials, sterile with one particular and 

 far from impotent bull, but not with another bull. But it 

 is too long a story — it is to attempt to make two strains, 

 both fertile, and yet sterile when one of one strain is 

 crossed with one of the other strain. But the difficulty 

 . . . would be beyond calculation.' :: 



The experiment was evidently unsuccessful, — perhaps 



1 More Letters, vol. i, pp. 231, 232, Letter 157. 



2 Ibid. vol. i, pp. 223, 224, Letter 153, [1862, December] 27. 



3 Ibid. vol. i, pp. 225, 226, Letter 154. 



