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THE AMEBIC AX NATURALIST [Vol. LII 



differences relate to a considerable range of more or less 

 independently varying characters, affecting both the in- 

 tensity and the extensity of the pigment in the hair and 

 skin. They are found to be, in a general way, correlated 

 with certain elements of the physical environment, while 

 the structural differences do not appear to be so corre- 

 lated. 



2. All of these differences, structural and pigmental, 

 are found to be differences of degree, revealed through a 

 comparison of mean or modal conditions rather than of 

 individual animals. In comparing the less divergent of 

 these races with one another, the frequency polygons for 

 any given character overlap broadly. 



3. These subspecific differences, and even the minor 

 differences which distinguish one narrowly localized sub- 

 race from the parent form, are found to be hereditary, as 

 evidenced by their persistence when environmental con- 

 ditions are interchanged. 



4. The gradations in certain of these characters by 

 which individuals of the same race differ from one an- 

 other are found to be strongly hereditary. 



5. Hybrids between even the most divergent of these 

 four races are predominantly intermediate in character, 

 both in the F x and the F 2 generations. In both of these 

 generations a wide range of variability is exhibited, which, 

 however, is little if any greater in the F 2 than in the F\. 



(5. In contrast to the sensibly continuous variation and 

 sensibly blended inheritance shown in respect to these 

 subspecific characters, is the behavior of certain "muta- 

 tions." Here we meet with typical discontinuous varia- 

 tion, and inheritance of the strictly alternative or Men- 

 delian type. It is insisted that the burden of proof rests 

 upon those who contend that these two types of variation 

 and inheritance are reducible to a single category, that of 

 discontinuity. Anything like a proof of this contention 

 appears to be thus far lacking. 



Supplementary Note (July 23, 1918). 

 It gives me pleasure to call attention to points of close 

 similarity between certain of the views expressed in the 



