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THE AMERICAN NATURALIST [Vol. XLIII 



carried by one body and the color producer' by a different one, 

 C G 



the pairs of allelomorphs will be c > (i ; every gray mouse carries 

 these two pairs which separate at some time in the germ cells so 

 that each germ cell (egg or sperm) carries one of each, C, G. 

 Now an albino must arise by failure of a germ cell to contain C, 

 the germ cell is simply (zero) G, but since the same body that 

 carried C may still be present (only one of its characters, namely 

 C, being absent) the presence of that body is represented by A. 



Let us now work out the case a step further. If this germ 

 cell, AG, combines in fertilization with another germ cell, CG, 

 of another individual, the resulting individual will be CGAG. 

 The allelomorph pairs will be ^, 2. If such a mouse again 

 pairs with a gray one, only gray mice will result. In time, 

 however, enough mice of the formulae CGAG will arise so that 

 two such may meet; then and only then will an albino mouse 

 appear amongst the gray offspring. Thus the conditions that ^ 

 produce the albino must arise two or more generations before 

 the actual albino mouse is discovered. 



This example shows, on the theory, how sports of this kind 

 (recessive) that appear in nature are due to conditions that 

 arise in the germ cells of an individual several generations 

 earlier. The only possibility, on the theory, that such recessive 

 sports could appear at once would be when several individuals 

 changed in the same direction at the same time. Then the possi- 

 bility of two germ cells of the same kind meeting would be 

 realized. Recognizing the rarity of the appearance of sports, 

 one may hesitate to assume that two such forms appear at the 

 same time and pair with each other. 



This view is based on the assumption that sports arise by the 

 dropping out of one character in a germ cell. If the absent 

 characters arise in some other way, after the germ cells have met 

 for example, the situation is different, but the assumptions here 

 made are in conformity with present-day development of Men- 

 delian inheritance. 



Our case was selected, however, not to illustrate how recessive 

 sports arise and later appear, but to show how absent factors 

 may be represented by bodies that in hybridizing become the 

 partners of bodies containing that factor. Hence the supposed 

 advantage of representing such absent factors by a definite 



