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THE AMERICAN NATURALIST [Vol. XLV 



periments designed to confirm the Lamarckian view 

 have given as yet negative results, even though these 

 may be called "promising," as he says. So all the evi- 

 dence of his breeding experiments is in reality quite in 

 favor of our genotype-conception! 



But how much depends upon our mental eyesight, 

 what we see. Woltereck confesses openly his belief in 

 continuous evolution and remarks that for a convinced 

 selectionist of the Weismann school the new genotype- 

 conception is a "hard blow." The aim of his paper in 

 question is to parry off such blows. Of course this parry 

 can not use his own statements just mentioned; as to 

 their obvious but inconvenient accordance with our con- 

 ception Woltereck might apply the famous words from 

 Harvey's times: "video sed non credo." Hence the 

 arguments must be taken from other observations, and 

 some very instructive results of cultures under varying 

 conditions have supplied the piece de resistance for the 

 discussion. Woltereck is within his right when assert- 

 ing that we consider different genotypes as having con- 

 stant differences (like different formulas in chemistry). 

 This is an essential point; but Woltereck, admitting no 

 constancy in the differences, tries to demonstrate that 

 our view must be fallacious. 



In a very suggestive manner he presents "phenotype- 

 curves" for several pure strains. These curves are 

 graphical schemes expressing (for the strain in ques- 

 tion) the average degree or intensity of any particular 

 character as it manifests itself under different condi- 

 tions, e. g., the relative length of heads by poor, inter- 

 mediate and rich feeding, etc. Such "phenotype- 

 curves" may indeed be very useful as records of the 

 behavior of the organisms in question, and they mark 

 certainly a valuable progress in descriptive methods. 



The phenotype-curves of the Daphnias in question 

 sometimes show rather constant differences between the 

 pure strains compared ; but mostly this is not the case. 

 Especially under extreme conditions, e. g., with poor or 

 even with very rich feeding, some of the curves are con- 



