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THE AMERICAN NATURALIST [Vol. XLIX 



pink, mixed and white flowers in the second (F 2 ) genera- 

 tion. New combinations had arisen, but only as an ex- 

 pression of that which already existed in the phenotypes, 

 for there is no evidence of an increase in unit characters 

 nor was there an actual increase in variability. 



There are only three papers of a statistical nature in 

 which it has seriously been asserted that cross-bred forms 

 or conjugating forms produced greater variability than 

 resulted in close-bred forms or non-conjugating forms. 



The first is that of Castle, Carpenter, Clark, Mast and 

 Barrows ('06) based on a series of observations as to the 

 effect of cross breeding and close breeding on the varia- 

 bility and fertility of the small fruit fly Drosophila 

 ampelophila Loew. In conclusion it was stated that 

 " inbreeding did not affect the variability in the number 

 of teeth of the sex comb of the male, nor the variability 

 in size," the first opinion resulting from the value of the 

 coefficient of variation in the number of tibial spines, the 

 second from the standard deviation in the length of the 

 tibia. In the former case the data certainly do not 

 permit a clear conclusion one way or the other. In the 

 second case, however, if the value of the coefficient of 

 variation is computed for the length of the tibia — which, 

 strange to say, was not done in the original investiga- 

 tion — and thus allowance made for the greater length of 



TABLE X 



Variation for '. 

 '. = Standard De< 



[.7L':ii.OM> 4.452.) 



