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THE AMERICAN NATURALIST [Vol. XLV 



that some organisms of identical genotypical constitution 

 are developing under different external conditions, then 

 these differences will produce more or less differences as 

 to the personal qualities of the individual organisms. By 

 simple inspection of series of different individuals it will 

 be quite impossible to decide if they have or have not the 

 same genotypical constitution — even if we know them to 

 be homozygotic. 3 AVe may easily find out that the organ- 

 isms in question resemble each other so much that they 

 belong to the same "type" (in the current sense of this 

 word), or we may in other cases state that they present 

 a disparity so considerable that two or more different 

 "types" may be discerned. 



All "types" of organisms, distinguishable by direct 

 inspection or only by finer methods of measuring or 

 description, may be characterized as "phenotypes." 

 Certainly phenotypes are real things; the appearing (not 

 only apparent) "types" or "sorts" of organisms are 

 again and again the objects for scientific research. All 

 typical phenomena in the organic world are eo ipso 

 phenotypical, and the description of the myriads of 

 phenotypes as to forms, structures, sizes, colors and other 

 characters of the living organisms has been the chief aim 

 of natural history, which was ever a science of essentially 

 morphological-descriptive character. 



Morphology, supported by the huge collections of the 

 museums, has of course operated with phenotypes in its 

 speculations concerning phylogenetic questions. The 

 idea of evolution by continuous transitions from one 

 "type" to another must have imposed itself upon zoolo- 

 gists and botanists, because the varying external condi- 

 tions of life are often 4 shifting the phenotypes in very 

 fine gradations ; but also— and that is an important point 

 —because there may always be found considerable geno- 

 typical differences hidden in apparently homogeneous 

 populations, exhibiting only one single "type" around 



4 Not always, as Bateson has the merit of having emphasized. 



