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THE AMERICAN NATURALIST [Vol. XLVI1I 



horns but one factor is insufficient in the females. This 

 conclusion was put to the test by breeding an F x hornless 

 ewe to a hornless ram. The Y 1 ewe should be hetero- 

 zygous for the factor for horns, and, therefore, when she 

 is bred to a homozygous hornless ram, half of her off- 

 spring should be heterozygous for hornlessness and half 

 homozygous for hornlessness. Since half of her sons 

 should have a factor for horns they are expected to 

 develop horns, and this is what occurred. Half of the 

 daughters also should have a factor for horns, but should 

 not develop horns, and this also was true. 



It has been recognized for several years that this and 

 related cases can not be explained on the assumption that 

 the factors involved are carried by the X or by the Y 

 chromosomes. But we can interpret the statement that 

 one factor for horns is sufficient in the males to call forth 

 horns, but not sufficient in the female "in terms of chromo- 

 somes," if a factor for horns is carried by one of the 

 chromosomes other than the sex chromosome. In other 

 words we need only appeal to a mechanism with which we 

 .are familiar to cover the results. 



The second illustration is furnished by the recent 

 experiments of Foot and Strobell, and since the authors 

 have rejected the chromosome hypothesis as inapplicable 

 to their results, and since in the case of insects the condi- 

 tions are simplified because castration experiments have 

 shown that the sex glands are not themselves responsible 

 for the secondary sexual characters, we may profitably 

 consider this case even more fully. 



In one of tlie bugs, Ew-histns rariolarius, the male has 

 a black spot on the abdomen. The female lacks the spot. 

 A female of this species was crossed to a male of another 

 species, viz., Euchistus servus, having no spot in either 

 sex. The daughters had no spot, the sons had a spot 

 fainter than that of variolar ins. Inbred these gave, in F 2 , 

 249 females without a spot, 107 males with a spot (devel- 

 oped to different degrees) and 84 males without a spot. 

 The F 1 results show that one factor for spot in the male 



