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dispenses with the services of the " unknown cause." 

 This is the modus opera?idi of an able scientist who 

 has not a pet theory, to which a recognition of the 

 competency of the known cause, to cover all of the 

 facts, threatens, instant explosion. This, however, is 

 not the mode of research of a scientist, who has a 

 theory of the character mentioned. This is not, as is 

 manifest, the mode of Darwin. All of the phenomena 

 of variation, are, as he concedes, with an unimportant 

 qualification, possible to be ranged under his second 

 head, viz., Reversion ; and there is not a single fact, to 

 be found in any of his works, or within the range of 

 physiology, .which militates against such a course. 

 But, should he so arrange them, and dispense with his 

 " unknown causes," with his " innate tendency," etc., in 

 which he fancies he has at least a ghost of a chance of 

 salvation for his theory; where would be even his 

 flimsy semblance of support for the hypothesis of in- 

 definitely continued development ? — of variation with- 

 out any assignable limit ? One, disposed to suspicion, 

 and to invidious comment, might doubtless assert, that 

 Darwin saw there was no earthly necessity for his class 

 of " unknown causes," and that, to preclude the im- 

 mediate dissolution of his theory, into the thinnest of 

 air, with " infinite dexterity of wit," threw in the fol- 

 lowing remark, to occasion a bewildering doubt, in his 

 readers' minds, as to whether the problem of the cause 

 of variation, was so simple as it really is. He says, 

 immediately subsequent to his elaboration of the two 

 heads mentioned, 



" But these two main divisions can often be only 



