HEREDITY AND MENDEL's LAW 185 



in the second hybrid generation does taillessness appear, and of 

 the JNIendelian segregation in the second hybrid generation there 

 is no trace ! On the other hand, another cock reveals typical 

 Mendelian phenomena. 



Finally, I will speak of a case which is perhaps most instruc- 

 tive of all. I crossed together a double-comb and a single- 

 comb, and a Polish with a V-comb. The hybrids have a new 

 type of comb called Y-comb ; single in front like the stem of a Y 

 and cleft behind like the Polish. Now in the first generation 

 the proportion of the single and the double element varies. At 

 one extreme the single element constitutes 5 per cent. ; at the 

 other extreme 95 per cent. Next, I bred together in various 

 generations some of these hybrids with Y-comb birds and, sum- 

 marizing the results, I found, out of several hundred progeny, 

 about 25 per cent, single comb, 25 per cent. V-comb and 50 per 

 cent. Y-comb. But when I came to examine the families in de- 

 tail it appeared that whenever both parents had a large propor- 

 tion of the single in their Y-comb, the proportion of a single- 

 combed offspring rose from 25 per cent, to 40 per cent., or even 

 50 per cent. ; and when the parents had a small proportion of 

 single in their Y-comb, the proportion of single-combed offspring 

 fell from 25 per cent, to 20 per cent. The 25 per cent, of single- 

 comb that one gets on the average seems to prove the Mendelian 

 doctrine of pure germ cells ; but the fact that when the tendency 

 to comb in parent is strong, 40 per cent, of the offspring have 

 single-comb ; when weak only 20 per cent., throws doubt on the 

 Mendelian doctrine of purity, and hints at a law of relative 

 potency. 



In the foregoing I have described the typical Mendelian phe- 

 nomenon and also various cases of deviation from it — cases of 

 contamination of the so-called pure type extracted from hybrids 

 — cases of lack of dominance, but of particulate or blending 

 inheritance ; and cases of potency of one unit character over its 

 antagonist — a potency not constant but varying with the indi- 

 vidual or with the strain. Taking all cases into account it is 

 clear that Mendel's law does not cover all ; and, if not, it must 

 be a special case of a more inclusive law. 



Can we find a more general expression for the inheritance of 



