DIAGNOSIS REQUIRES CONFIRMATION 77 



Jordan, ' The actual proof of specific distinctness the 

 systematist as such cannot bring ; ... we work, or we 

 ought to work, with the mental reservation that the 

 specific distinctness of our species novae deduced from 

 morphological differences will be corroborated by bio- 

 logy.' 1 



The advantage of this attitude is obvious. Work 

 would go on as at present. Powers of acute observation 

 and good judgement would still furnish descriptions of 

 species to be hereafter confirmed or confirmed at the 

 $ime by observation and experiment upon the living 

 material. But the systematist would not only receive 

 our gratitude for the performance of these important and 

 necessary duties : he would also be seeking in every 

 direction for the evidence of Syngamy and of Epigony. 

 The museum would become a centre for the inspiration 

 of researches of the highest interest to the investigator 

 himself, of the greatest importance to the whole body 

 of naturalists. 



Interspecific Sterility as a test of Species. 



We now turn to the consideration of interspecific 

 sterility, which many have supposed to be an infallible 

 criterion. Huxley himself felt this so strongly that he 

 was, in consequence, never able to give his full assent 

 to Natural Selection. The grounds of his objection were 

 the subject of prolonged correspondence with Darwin. 

 In order to prove that Natural Selection has produced 

 natural species separated rigidly, as he believed, by the 

 barrier of sterility, Huxley maintained that we ought to be 

 able to produce the same sterility between our artificially 

 selected breeds ; and until this had been done he could 

 not thoroughly accept the theory of Natural Selection. 

 This objection he expressed, or implied, in many speeches 

 and writings up to within a few months of his death. One 

 of the simplest statements is contained in a letter to the 

 late Charles Kingsley. Huxley wrote, April 30, 1863 : — 



1 Novitates Zoologicae, vol. iii, December, 1896, pp. 450, 451. I here 

 desire to express my indebtedness to the author of this learned and valuable 

 paper. 



