Charles Benedict Davenport

In my 1906 report I described in detail the form of the nostril in poultry. Usually it is closed down to a narrow slit, but in some races, as, e. g., the Polish and Houdans, the closing flap of skin fails to develop and the nostril remains wide open. This is apparently an embryonic condition. Thus in Keibel and Abraham's (1900) Normaltafeln of the fowl it is stated that the outer nasal opening, which is at first wide open, becomes closed with epithelium at about the middle of the sixth day of development. The Polish and Houdan fowl thus retain in the outer nasal opening an embryonic condition. The question is: How does this embryonic, open condition of the nostril behave in heredity with reference to the more advanced narrow-slit condition?

The wide-nostriled races used were both the Polish and the Houdan. The condition of the external nares is much the same in the two, but is slightly more exaggerated in the Houdans than in the Polish. The open nostril is often associated with a fold across the culmen, apparently due to the upturning of the anterior end of the premaxillary process of the nasal bone. Breeders of Houdans have sought to exaggerate the height of the fold. In both races there is great variability in the degree of "openness" of the nostril, and to indicate this I have adopted a scale of 10 grades (running from 1, the narrowest, to 10, the widest). To get some idea of this variability let us consider the grade of nostril in some families of pure Houdans.

Table 45.—Variability (expressed in decimal grades) of the degree of "openness" of the nostrils in families of "pure-bred" Houdans.

Serial No.	Pen No.	Mother.		Father.		Grade of openness in offspring.
		No.	Grade.	No.	Grade.	1	2	3	4	5	6	7	8	9	10
1	727	2457	9	831	10	...	...	...	...	...	...	...	...	5	4
2	727	2459	10	831	10	...	...	1	...	...	...	1	3	7	3
3	727	2494	9	831	10	...	...	...	...	...	...	...	...	1	4
4	727	3105	9	831	10	...	1	...	1	2	1	...	5	7	3
5	727	3106	9	831	10	...	...	...	...	...	...	...	...	2	1
6	803	2457	8	7522	9	...	1	1	...	...	2	4	7	10	3
7	803	2459	10	7522	9	...	...	...	...	...	...	1	6	4	2
8	803	3105	9	7522	9	1	...	...	...	4	2	2	7	3	7
	Totals (119)					1	2	2	1	6	5	8	28	39	27
	Percentages.					5.3				5.3	4.4	7.1	24.8	34.5	23.9

Table 45 shows that the prevailing grade in the offspring of pure Houdans is 9; that grades 8 and 10 are also extremely common; and that lower grades, even down to 1, may occur, but these are much less common. We have next to consider the grade-distribution of the offspring of the narrow mated with the wide nostril.

Table 46.—Distribution of the frequency of the different grades of "openness" of nostril when one parent has the open nostril and the other the closed.

[A] Extracted D × R.
Serial No.	Pen No.	Mother.				Father.				Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.	1	2	3	4	5	6	7	8	9	10
9	727	121	P.	Dk. Brahma.	1	831	P.	Houdan	10	9	11	6	6	2	3	1	1	...	...
10	735	142	P.	Mediterran.	1	30	P.	Polish	8	4	1	...	...	...	...	...	...	...	...
11	735	177	P.	Do.	1	30	P.	Do.	8	...	4	2	1	...	...	...	...	...	...
12	735	198	P.	Do.	1	30	P.	Do.	8	...	3	1	...	...	1	...	...	...	...
				Totals (56)						13	19	9	7	2	4	1	1	...	...
				Percentages						23.2	34.0	16.1	12.5	3.6	7.1	1.8	1.8	...	...
[A]12a	813	912	F2	Houd × Legh.	2	3904	F2	Houd × Legh.	7	3	10	3	1	1	...	...	...	...	...

Table 46 gives us a picture of the nature of the dominance in this case. At first sight the narrow nostril, grades 1 and 2, including 57 per cent of the offspring, appears to be dominant. But, as later evidence shows, it is recessive. The wide nostril is dominant, but so imperfectly that only 10 per cent have a nostril above one-half open.

Let us now consider the distribution of nostril form in families whose parents are hybrids of the first or later generation, crossed respectively on recessives, heterozygotes, and dominants (tables 47-49).

Table 47.—Distribution of frequency of the different grades of "openness" of nostril when one parent is heterozygous and the other recessive, i. e., with closed nostril (DR × R).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Race.	Gr.		1	2	3	4	5	6	7	8	9	10
13	768	298	F2	Med. × Polish	2	1689	P.	Med.	1	3	11	9	3	1	3	...	1	...	...	...
14	768	509	F1	Do.	1	1689	P.	Do.	1	2	12	5	6	1	1	...	...	...	...	...
				Totals (53)							23	14	9	2	4	0	1	...	...	...
				Percentages							43.4	26.4	17.0	3.8	7.6	...	1.9	...	...	...

The study of the tables 45 to 54 establishes the following conclusions:

First, high nostril is dominant. This means that there is a factor that inhibits the development of the narial flap. In the absence of such a factor the flap goes on developing normally. This hypothesis is opposed to the conclusion that I reached in my report of 1906 (pp. 68, 69). I there said:

A close agreement exists between the percentage obtained in each generation and the expectation of the Mendelian theory, assuming that narrow nostril is dominant. The statistics do not, however, tell the whole story. In 36 per cent of the cases in the F₁ generation the nostril was wider than in the "narrow" ancestor. Even in the F₂ generation nearly half of the "narrow and intermediate" were of the intermediate sort. This intermediate form is evidence that dominance is imperfect and segregation is incomplete.

Table 48.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (DR × DR).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
15	802	5314	F1	Polish × Min.	3	6652	F1	Polish × Min.	4	7	1	5	5	...	...	1	...	...	3	1
16	805	5307	F1	Do.	5	4799	F1	Do.	2	7	7	7	13	3	7	1	...	2	2	1
17	852	5104	F1	Hou. × Dk. Br.	3	5969	F1	Hou. × Dk. Br.	3	6	4	11	4	2	1	1	1	...	...	...
18	805	4800	F1	Polish × Min.	3	4799	F1	Polish × Min.	2	5	10	13	9	1	2	8	...	1	2	...
19	805	5308	F1	Do.	3	4799	F1	Do.	2	5	3	7	3	2	1	...	...	...	...	...
21	759	797	F1	Houd. × Min.	3	570	F1	Houd. × Min.	2	5	2	4	2	2	...	...	...	...	...	2
22	759	797	F1	Do.	3	352	F1	Do.	1	4	...	2	2	...	...	...	...	...	1	1
23	805	4447	F1	Polish × Min.	2	4799	F1	Polish × Min.	2	4	6	5	4	...	2	...	1	1	3	...
24	805	4765	F1	Do.	2	4799	F1	Do.	2	4	5	12	4	2	1	1	2	...	2	...
25	805	4797	F1	Do.	2	4799	F1	Do.	2	4	4	2	6	...	...	...	...	1	...	...
26	805	5163	F1	Do.	2	4799	F1	Do.	2	4	7	17	13	4	1	2	2	2	1	...
27	805	5304	F1	Do.	2	4799	F1	Do.	2	4	5	9	8	...	1	...	...	...	...	...
28	852	7070	F1	Hou. × Dk. Br.	1	5969	F1	Hou. × Dk. Br.	3	4	4	11	4	2	1	1	1	...	...	...
29	759	529	F1	Houd. × Min.	2	570	F1	Houd. × Min.	2	4	2	3	...	...	...	...	...	...	...	1
30	759	529	F1	Do.	2	352	F1	Do.	2	4	1	3	...	...	...	...	...	...	...	...
31	728	174	F1	Hou. × Wh.L.	1	258	F1	Hou. × Wh.L.	2	3	2	7	2	1	1	1	1	...	...	...
32	805	4798	F1	Polish × Min.	1	4799	F1	Polish × Min.	2	3	7	10	3	2	1	2	...	4	2	...
33	805	5323	F1	Do.	1	4799	F1	Do.	2	3	17	7	2	...	...	1	...	2	1	...
				Totals (435)							92	147	88	21	22	19	10	13	17	6
				Percentages							21.2	33.8	20.2	4.8	5.0	4.4	2.3	3.0	3.9	1.4

Table 49.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (DR × DR, F₂ and later generations).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
34	763	3799	F2	Hou. × Wh. L.	6	2247	F2	Hou. × Wh. L.	2	8	...	2	2	2	2	...	1	...	...	...
35	765	84	F1	Do.	3	1794	F2	Do.	5	8	1	6	8	1	4	1	1	2	6	3
36	765	984	F2	Do.	3	1794	F2	Do.	5	8	8	3	1	2	2	1	0	2	5	...
37	802	4013	F2	Polish × Min.	4	6652	F1	Polish × Min.	4	8	6	12	9	6	...	...	...	1	1	1
38	802	3954	F3	Do.	3	6652	F1	Do.	4	7	4	12	3	2	1	...	2	6	9	1
39	802	4038	F2	Do.	3	6652	F1	Do.	4	7	3	8	4	3	2	...	1	4	1	1
40	802	4164	F2	Do.	3	6652	F1	Do.	4	7	6	8	6	2	1	1	...	2	2	2
41	812	84	F1	Hou. × Wh. L.	3	4118	F3	Hou. × Wh. L.	4	7	...	1	5	2	2	1	1	1	1	2
42	812	913	F2	Do.	3	4118	F3	Do.	4	7	10	6	6	1	...	...	...	3	2	5
43	812	4728	F3	Do.	3	4118	F3	Do.	4	7	8	5	5	1	5	2	2	2	9	2
44	812	5120	F3	Do.	3	4118	F3	Do.	4	7	1	2	2	...	1	...	...	...	1	2
45	812	5540	F3	Polish × Min.	3	4118	F3	Do.	4	7	2	5	6	1	1	...	...	...	...	...
46	763	2250	F3	Hou. × Wh. L.	5	2247	F2	Do.	2	7	4	10	2	...	...	...	...	1	0	2
47	812	4726	F2	Do.	2	4118	F3	Polish × Min.	4	6	4	6	3	...	2	1	...	2	1	3
48	812	4735	F2	Do.	2	4118	F2	Do.	4	6	2	1	1	...	...	...	...	2	1	...
49	765	1790	F3	Do.	1	1794	F2	Hou. × Wh. L.	5	6	9	14	9	1	3	0	2	0	3	...
50	802	4012	F3	Polish × Min.	1	6652	F1	Polish × Min.	4	5	5	13	11	3	2	...	1	3	1	...
51	825	2198	F3	Do.	3	3852	F3	Do.	2	5	...	...	1	3	...	...	...	...	...	1
52	728	2271	F2	Hou. × Wh. L.	3	258	F1	Hou. × Wh. L.	2	5	4	3	1	7	2	1	3	1	1	2
53	763	2700	F2	Do.	3	2247	F2	Do.	2	5	1	2	3	3	...	1	...	...	2	...
54	825	350	F1	Polish × Min.	2	3852	F3	Polish × Min.	2	4	4	13	6	4	...	...	...	3	1	3
55	825	4708	F3	Do.	2	3852	F3	Do.	2	4	4	13	7	3	...	1	1	1	2	3
56	825	5019	F2	Do.	2	3852	F3	Do.	2	4	1	1	...	...	...	...	...	1	2	2
57	825	5035	F3	Do.	2	3852	F3	Do.	2	4	4	...	3	1	1	...	...	1	1	1
58	825	5672	F3	Do.	2	3852	F3	Do.	2	4	1	3	2	...	2	...	...	1	2	1
59	728	2248	F2	Hou. × Wh. L.	2	258	F1	Hou. × Wh. L.	2	4	3	6	7	2	...	...	1	0	1	3
61	763	377	F1	Do.	1	2247	F2	Do.	2	3	20	9	14	3	6	0	2	0	2	1
				Totals (663)							115	641	127	53	39	10	8	39	57	41
				Percentages							17.4	24.7	19.2	8.0	5.9	1.5	2.7	5.9	8.6	6.2
											69.3				30.7

These earlier data were not even roughly quantitative, and it is the quantitative data that first give the key to the true relations. However, sufficient evidence for the change in the conclusion is certainly due. The evidence is found in a careful study of table 55, keeping constantly in mind this fundamental principle that the recessive condition alone in the parents can never give rise to the dominant; for the recessive condition implies entire absence of the dominant factor. But the pure dominant condition will vary in the direction of the recessive condition; such a result implies only a partial failure of the factor to develop completely; and we should not be surprised if occasionally the failure were complete. This implies no "reversal of dominance," but rather an arrested development of the factor.

Table 50.—Distribution of frequency of grades of "openness" in offspring when one parent is heterozygous and the other an original dominant (DR × D, originals).

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
62	803	529	F1	Houd. × Min.	3	7522	P.	Houd.	9	12	4	2	4	1	2	...	...	2	2	1
63	803	7065	F1	Houd. × Dk. Brah.	1	7522	P.	Do.	9	10	6	11	6	4	2	1	2	6	4	1
				Totals (61)							10	13	10	5	4	1	2	8	6	2
				Percentages							16.4	21.3	16.4	8.2	6.5	1.6	3.3	13.1	9.8	3.3
											62.3				37.7

Table 51.—Distribution of frequency of grades of "openness" in offspring when one parent is heterozygous and the other an extracted dominant (DR × DD, extracted).

[Abbreviations: H = Houdan; L = Leghorn; M = Minorca; P = Polish; WL = White Leghorn.]

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
64	832	4404	F3	H × WL	4	5119	F3	H × WL	10	14	1	1	1	2	...	...	...	8	1	1
65	729	913	F2	Do.	6	936	F2	Do.	10	16	5	6	16	2	5	...	3	11	11	10
66	819	57	F1	P × M	4	1420	F2	P × M	10	14	3	2	4	...	...	1	...	3	5	1
67	832	505	F1	(H × L)L	4	5119	F3	H × WL	10	14	2	2	3	3	2	...	2	2	2	4
68	729	935	F2	H × WL	4	936	F2	Do.	10	14	3	5	4	0	3	2	5	12	15	3
69	756	2011	F2	HPMWL	4	444	F2	Do.	10	14	...	...	...	1	...	1	...	1	4	3
70	807	185	F1	P × M	4	3894	F3	P × M	9	13	4	2	...	...	...	2	1	1	2	1
71	756	1048	F2	Do.	3	1390	F2	Do.	10	13	...	...	3	...	...	...	...	...	2	...
72	762	505	...	(H × L)L	3	444	F2	H × L	10	13	1	1	3	1	1	2	2	2	3	4
73	762	2011	F3	HPML	4	2621	F2	HPML	9	13	...	1	...	...	...	...	1	1	3	1
74	813	2271	F2	H × WL	5	3904	F3	H × WL	7	12	1	5	5	2	2	1	3	2	4	9
75	820	984	F2	H × L	3	4731	F3	P × M	9	12	...	5	4	2	5	1	...	5	5	4
76	728	2272	F2	Do.	10	258	F1	H × L	2	12	2	7	9	4	4	3	2	7	7	9
77	756	1043	F2	P × M	2	1390	F2	P × M	10	12	5	5	3	2	...	...	...	3	2	2
78	762	505	...	(H × L)L	3	2621	F3	HPML	9	12	1	...	...	...	...	1	...	...	...	3
79	803	2250	F2	H × L	3	7522	P.	Houd.	9	12	...	5	2	2	4	...	...	4	9	6
80	803	2254	F2	Do.	3	7522	P.	Do.	9	12	6	6	4	1	2	1	1	3	6	3
81	769	492	F1	Do.	2	911	F2	H × L	9	11	3	6	1	1	...	2	...	...	1	...
82	807	1043	F3	P × M	2	3894	F2	P × M	9	11	9	4	2	...	3	3	...	6	6	...
83	769	2254	F2	H × L	1	911	F2	H × L	9	10	7	7	2	1	...	...	1	2	4	1
84	813	935	F2	Do.	3	3904	F3	Do.	7	10	1	2	...	4	4	3	...	7	8	1
85	813	5113	F3	Do.	3	3904	F3	Do.	7	10	4	5	5	...	1	1	1	6	8	5
86	813	5142	F3	Do.	3	3904	F3	Do.	7	10	...	2	...	...	...	...	...	1	1	3
87	813	5122	F3	Do.	2	3904	F3	Do.	7	9	...	1	2	...	1	...	...	2	2	3
88	813	7320	F3	Do.	2	3904	F3	Do.	7	9	...	6	1	...	1	...	...	2	5	2
89	813	377	F1	Do.	1	3904	F3	Do.	7	8	10	...	6	1	...	...	1	4	3	...
				Totals (641)							68	86	80	29	38	24	23	95	119	79
				Percentages							10.6	13.4	12.5	4.5	5.9	3.7	3.6	14.8	18.6	12.3
											41.0				59.0

Table 52.—Distribution of frequency of grades of "openness" in offspring when both parents are extracted dominants (extracted DD × DD).

[Abbreviations: H = Houdan; L = Leghorn; M = Minorca; P = Polish; WL = White Leghorn.]

Serial No.	Pen No.	Mother.				Father.				Total gr.	Grade of openness in offspring.
		No.	Gen.	Races.	Gr.	No.	Gen.	Races.	Gr.		1	2	3	4	5	6	7	8	9	10
91	729	2016	F2	HPLM	10	936	F2	H × L	10	20	...	...	...	...	...	...	...	4	6	5
92	729	2255	F2	H × L	10	936	F2	Do.	10	20	3	3	...	...	...	1	2	5	11	10
93	729	2269	F2	Do.	10	936	F2	Do.	10	20	...	1	...	...	...	1	...	3	9	13
94	729	2324	F2	HPLM	10	936	F2	Do.	10	20	2	3	...	...	1	1	...	5	16	7
95	756	1067	F2	P × M	10	1390	F2	P × M	10	20	...	1	3	2	1	...	...	1	1	...
96	756	1113	F2	Do.	10	1390	F2	Do.	10	20	...	...	...	...	...	...	1	4	8	4
97	762	2014	F3	HPLM	10	444	F2	H × L	10	20	...	...	...	...	...	...	...	...	1	4
98	819	1113	F2	P × M	10	1420	F2	P × M	10	20	...	...	...	...	...	...	...	2	6	2
99	819	4257	F3	Do.	10	1420	F2	Do.	10	20	...	...	2	...	...	...	...	4	4	3
100	832	4732	F3	H × L	10	5119	F3	H × L	10	20	...	...	...	...	...	...	...	2	1	...
101	832	6481	F3	Do.	10	5119	F3	Do.	10	20	...	...	...	...	...	...	...	2	5	4
102	756	369	F2	P × M	9	1390	F2	P × M	10	19	...	2	...	...	...	...	...	...	1	1
103	762	2618	F2	HPLM	9	444	F2	H × L	10	19	...	...	...	...	...	...	...	1	1	...
104	762	3776	F2	H × L	9	444	F2	Do.	10	19	...	...	...	...	...	...	...	1	1	...
105	832	5803	F3	Do.	9	5119	F3	Do.	10	19	...	...	1	1	...	...	1	6	9	6
106	807	1067	F2	P × M	10	3894	F3	P × M	9	19	...	1	1	1	2	1	2	1	4	2
107	762	2333	F3	HPLM	8	444	F2	H × L	10	18	...	...	...	...	...	...	1	2	5	4
108	762	2618	F2	Do.	9	2621	F3	HPLM	9	18	...	...	...	...	...	...	...	1	2	2
109	762	3776	F2	H × L	9	2621	F3	Do.	9	18	...	...	...	...	1	...	2	4	4	...
110	819	5674	F2	P × M	8	1420	F2	P × M	10	18	1	...	1	...	...	...	2	1	3	2
111	820	2016	F2	HPLM	9	4731	F3	Do.	9	18	...	...	...	...	1	...	1	1	4	...
112	820	2255	F2	H × L	9	4731	F3	Do.	9	18	...	...	...	...	...	...	1	2	6	5
113	820	6479	F3	Do.	9	4731	F3	Do.	9	18	...	...	1	...	2	1	2	9	12	4
114	832	2618	F2	HPLM	8	5119	F3	H × L	10	18	1	1	3	4	...	...	...	...	12	3
115	832	3776	F2	H × L	8	5119	F2	Do.	10	18	...	3	3	...	2	...	...	...	...	...
116	834	2324	F2	HPML	9	5090	F2	Do.	9	18	...	1	...	...	...	1	...	10	10	3
117	762	2333	F3	HPLM	8	2621	F3	HPLM	9	17	...	...	...	...	1	...	1	...	...	1
118	807	5075	F2	P × M	7	3894	F3	P × M	9	16	...	1	...	...	2	1	...	5	7	7
119	820	5143	F3	H × L	7	4731	F3	Do.	9	16	1	1	2	5	...	1	3	10	10	12
120	813	2272	F2	Do.	9	3904	F3	H × L	7	16	1	1	1	...	1	...	2	5	7	7
				Totals (472)							9	19	18	13	14	8	22	93	169	105
				Percentages							1.9	4.0	3.8	2.8	3.0	1.7	4.7	19.8	36.0	22.3

Table 53.—Distribution of frequency of grades of "openness" in offspring when both parents are heterozygous (RR × DR).

Serial No.	Pen No.	Mother.				Father.				Grade of openness in offspring.
		No.	Gen.	Races.	Grade.	No.	Gen.	Races.	Grade.	1	2	3	4	5	6	7	8	9	10
121	728	174	F1	Houd. × Legh.	1	1258	P.	Brah. × Tosa.	2	2	7	2	1	1	1	1	...	...	...
122	728	912	F2	Do.	2	258	F1	Houd. × Legh.	2	7	3	3	2	1	...	...	...	...	...
123	763	3799	F1	Min. × Houd.	6	2247	F2	Do.	2	...	2	2	2	2	...	1	...	2	...
124	802	509	F2	Polish × Min.	1	6652	F1	Polish × Min.	4	6	6	1	...	1	...	...	...	...	...
125	802	3846	F2	Do.	2	6652	F1	Do.	4	1	6	3	1	1	...	...	...	...	...
126	802	5025	F3	Do.	2	6652	F1	Do.	4	8	10	4	3	2	...	...	...	...	...
127	802	5087	F3	Do.	2	6652	F1	Do.	4	7	9	12	2	...	1	...	...	...	1
				Totals (217)						31	43	27	11	8	2	2	0	2	1
				Percentages						24.4	33.9	21.3	8.7	6.3	1.6	1.6	0	1.6	0.8

Table 54.—Distribution of frequency of grades of "openness" in offspring when both parents are extracted recessives (extracted RR × RR).

[A] Cf. Serial No. 12a.

Serial No.

Pen No.

Mother.

Father.

Total gr.

Offspring.

No.

Gen.

Races.

Grade.

No.

Gen.

Races.

Grade.

Grade 1

Grade 2

128

728

[A]912

F2

Houd. × Legh.

2

1298

F2

Houd. × Legh.

1

3

3

3

129

827

298

F2

Pol. × Min.

2

3852

F3

Do.

2

4

5

5

At the outset, then, we find (table 55) that even pure races with high nostril (Polish, Houdans), when bred together, vary much in the height of nostril (in perfection of dominance) and, in 2 per cent of the offspring, even show the typical narrow nostril (fig. B, a). On the other hand, in the narrow-nostriled races I have never obtained any such variation. The most deviation that I have seen from grade 1 is found in my strain of Dark Brahma bantams that frequently give grade 2. The variability of the high nostril, the stability of the low nostril, is prima facie evidence that the former is due to the presence of a particular factor and the latter to its absence.

Next, the heterozygotes of F₁ (table 46), may be appealed to; but they will give no critical answer. For expectation, dominance being imperfect, is that the hybrids will be intermediate, and the result will be the same whichever extreme grade is taken as dominant. The empirical mode in the distribution of the offspring is at grade 2. This implies much greater imperfection of dominance on the hypothesis that grade 10 is dominant than on the hypothesis that grade 1 is dominant; but this very fact supports the former hypothesis, since imperfection of dominance is obviously a feature of the character with which we are dealing.

The critical test is afforded by the F₂ generation (tables 48 and 49). By hypothesis, 25 per cent of the offspring are expected to be pure ("extracted") recessives, and the same number pure dominants; and also, by hypothesis, the recessives are massed at or near one grade while the dominants are variable. Now, as a matter of fact, the upper 25 per cent range over 5 to 7 grades, while the lower 25 per cent are nearly massed in grade 1 (21 per cent are so massed in one table, 17 per cent in the other). Therefore, in accordance with hypothesis we must regard the lower grade—narrow slit—as recessive. Similarly, heterozygous × low nostril (table 47) should give, on our hypothesis, 50 per cent low nostril. If that is recessive we should expect a massing of this 50 in the first two grades; if dominant a greater scattering. The former alternative is realized. Again, in the heterozygous × high nostril hybrid (table 50) the upper 50 per cent will be massed or scattered according as high nostril is recessive or dominant. Allowing for the 50 per cent heterozygotes in the progeny, the 50 per cent of high nostrils are scattered through at least 8 grades of the possible 10. High nostril is dominant. Finally, extracted high nostrils bred together produce offspring (table 52) with a great range of variability (through all grades), while extracted low nostrils (unfortunately all too few) give progeny with grades 1 and 2 (table 53; fig. B, h). Accepting, then, the general principle of the greater variability of the dominant character, we have demonstrated conclusively that high nostril, or rather the factor that determines high nostril, is dominant.

Comparing tables 45 to 54, we see that recessive parents are characterized by a low grade of nostril and they, of course, tend to produce offspring with a low grade. Similarly, dominants have a high grade and tend to produce offspring of the same sort, while heterozygous parents are of intermediate grade and their children have nostril grades that are, on the average, intermediate. Without regarding the gametic constitution, we might conclude, with Castle, that offspring inherit the grade of their parents, and consequently it would be possible to increase the grade, perhaps indefinitely, by breeding from parents with the highest grade. Considering the gametic constitution of the parents, it is obvious that such a conclusion is premature. To get an answer to the question it is necessary to find if there is, inside of any one table, among parents of the same gametic constitution, any such relation between parental and filial grades. This can be determined by calculating the correlation between the grades of parents and progeny. Such calculation I have made for table 48 with the result: index of correlation, r=0.018±0.032, which is to be interpreted as indicating that no correlation exists; and in so far the hypothesis of Castle proves not to apply in the cases of booting and doubt is thrown on the significance of his conclusion.

Finally, if we throw together the frequency distributions of all tables into one table (table 55; compare fig. B) we shall find the totals instructive. Table 55 shows that, when all results are thrown together, including hybrids of all sorts, grade 2 and grade 9 are the most frequent and grade 6 is the least frequent, the frequency gradually rising towards the extremes of the series. The same result appears in the individual series that range from grade 1 to grade 10. What is the meaning of this result? It seems to me to bear but one interpretation, namely, that there are only two centers of stability—about grades 1 and 9—and true blending of these grades, giving an intermediate condition, does not occur. Otherwise, in consequence of the repeated hybridization, the intermediate grades must be the commonest instead of the rarest. There is alternative inheritance of the nostril height.

Table 55.—Summary of tables 45 to 54.