Januabt 18, 1907] 



SCIENCE 



107 



cause de cette determination reside-t-elle dans 

 la fecondation pour le sexe femelle, et dans 

 I'absence de fecondation pour le sexe male, il 

 se peut qu'il en soit ainsi, mais le fait n'est 

 pas demontre." 



On the other hand, Silvestri very definitely 

 determined that in the ease of Litomastix the 

 parthenogenetic development does take place 

 and that, as in the bees, the fertilized eggs 

 always give rise to females, the unfertilized 

 to males. Until further observations have 

 been made it would seem unsafe to discard 

 Bugnion's earlier hypothesis that the observed 

 facts regarding the preponderance of one sex 

 or the other in Encyrtus are to be likewise 

 explained. Wm. A. Kiley 



VARIATION OR MUTATION? 



Systematic zoologists are not likely to be 

 hasty in endorsing the dogma of de Vries in 

 respect of individual variations, or ' fluctua- 

 tions ' in his terminology: "* * * they may 

 be proved to be inadequate even to make a 

 single step along the great lines of evolution, 

 in regard to progressive as well as retrogres- 

 sive development." ' 



There are two methods of approach to the 

 part played by mutations and individual vari- 

 ations in the development of specific charac- 

 ters: the comparative, in use by taxonomists, 

 and the experimental, at the hands chiefly of 

 embryologists. 



The argument for individual variation from 

 the comparative side was well presented by 

 Dr. C. Hart Merriam, in his vice-presidential 

 address before the American Association, and 

 that for mutations from the experimental side, 

 with equal clearness, by Professor Davenport, 

 in Science of November 2, although he does 

 not take the extreme view of de Vries. 



Now, both systematist and experimenter 

 will admit the absence of any exact means of 

 determining what may or may not have been 

 originally a mutation in such cases, for in- 

 stance, as slight discontinuity observed under 

 nature where there is no knowledge of the 

 race history — for when Davenport asks : " But 

 will it not be often impossible to say whether 

 a new-appearing quality is truly new or 



' ' Species and Varieties,' p. 18, 1905. 



old ? " ' no one can deny him. The statistical 

 method, though it be fondly looked on as a 

 universal solvent, can give no help here, for 

 it points out only the end facts, not their 

 causes, and there seems to be no resource but 

 in the balanced judgment of competent ob- 

 servers. Therefore, when one so qualified as 

 Dr. Merriam states his opinion that in more 

 than a thousand species and subspecies of 

 North American mammals and birds, he does 

 not find one which appears to have arisen by 

 mutation, he records a conclusion of great 

 weight. Essential agreement with Merriam 

 results from a similar examination of North 

 American scaled reptiles. 



The measure established is that a species 

 or subspecies to be rated as a possible mutant 

 must be separated from its nearest known 

 congener by at least one indivisible character. 

 This, I believe, accords with the standard set 

 by de Vries, as well as with that of Professor 

 Davenport. It might be claimed by extreme 

 mutationists that monotypic genera, appearing 

 to be related to a species of another genus 

 occupying the same range, have arisen by mu- 

 tation, but in these cases there is rarely valid 

 evidence on either side, and as either view 

 must be an assumption, they are not consid- 

 ered in this examination. If we are to reach 

 a general rule of probability it must be 

 through cases determined upon reasonable 

 grounds. 



I have followed Professor Cope's last de- 

 scriptive 'list of Nearctic reptiles, not by any 

 means from complete agreement with it, but 

 for the reason that the analytic method fa- 

 vored by him left few variants unnamed. 



Among lizards. Cope says of the genus 

 Sceloporus: "I recommend it as an excellent 

 piece de resistance for those persons who do 

 not believe in the doctrine of the derivation 

 of species." This thought may be borrowed 

 and extended to include the whole list of 

 Nearctic lizards, and addressed to all who re- 

 quire evidence of the derivation of species by 

 minute gradations, for nowhere else, perhaps, 

 are they more general. There is no room here 

 for mutations. 



'Science, September 22, 1905, p. 370. 



