1864— 1869] WEISMANN 3 11 



receiving the " kleine Schrift" 1 to which you allude; but I Letter 226 

 fear it is lost, which I am much surprised at, as I have seldom 

 failed to receive anything sent by the post. 



As I do not know the title, and cannot order a copy, I 

 should be very much obliged if you can spare another. 



I am delighted that you, with whose name I am familiar, 

 should approve of my work. I entirely agree with what 

 you say about each species varying according to its own 

 peculiar laws ; but at the same time it must, I think, be 

 admitted that the variations of most species have in the lapse 

 of ages been extremely diversified, for I do not see how it 

 can be otherwise explained that so many forms have acquired 

 analogous structures for the same general object, indepen- 

 dently of descent. I am very glad to hear that you have 

 been arguing against Nageli's law of perfectibility, which 

 seems to me superfluous. Others hold similar views, but 

 none of them define what this " perfection " is which cannot 

 be gradually attained through Natural Selection. I thought 

 M. Wagner's first pamphlet 2 (for I have not yet had time to 

 read the second) very good and interesting ; but I think that 

 he greatly overrates the necessity for emigration and isolation. 

 I doubt whether he has reflected on what must occur when his 

 forms colonise a new country, unless they vary during the very 

 first generation ; nor does he attach, I think, sufficient weight 

 to the cases of what I have called unconscious selection by man : 

 in these cases races are modified by the preservation of the best 

 and the destruction of the worst, without any isolation. 



I sympathise with you most sincerely on the state of 

 your eyesight : it is indeed the most fearful evil which can 

 happen to any one who, like yourself, is earnestly attached 

 to the pursuit of natural knowledge. 



1 The " kleine Schrift " is " Ueber die Berechtigung der Darwin'schen 

 Theorie," Leipzig, 1868. The "Anhang" is "Ueber den Einfluss der 

 Wanderung und raiimlichen Isolirung auf die Artbildung." 



* Wagner's first essay, Die Darwirische Theorie und das Migra- 

 tionsgesetz, 1868, is a separately published pamphlet of 62 pages. In 

 the preface the author states that it is a fuller version of a paper read 

 before the Royal Academy of Science at Munich in March 1868. We 

 are not able to say which of Wagner's writings is referred to as the 

 second pamphlet; his second well-known essay, Ueber den Einfluss der 

 Geogr. Isolirung, etc., is of later date, viz., 1870. 



