240 
Back Cross ) 
6 632SX(? 106L+ 9 486L+ 9 501L+ 9 559L 
Simplex X Recessive 
The Journal of Heredity 
Offspring (1917 crop) 
Simplex X Recessive 
6 650S+ 9 651S+ 4 652L+ 4 654L 
6 6328S X (9 611L+ 9° 623L-+ 9? 624L 
4 653L & Matings 7 
Offspring 5S-3L 
Offspring (1917 crop) 
The result of these matings was five 
short and three long-eared individuals, 
the former being simplex and the latter 
pure recessive since they were derived 
from a simplex x recessive back cross. 
The following year, ram No. 650, a 
6 655S+ 4 656S+ 9 657S 
simplex offspring, was bred to the same 
list of ewes with the exception that ewe 
No. 616 replaced ewe No. 106, both 
pure recessives, with the result shown 
diagrammatically as follows: 
Back Cross 
Simplex x Recessive 
4 650S X (9 486L+ 9 501L+ 9 559L+ 9 611L | 
Offspring (1918 crop) 
Simplex & Recessive 
6 658S+ 6 659L+ 9 661L+ 9 662S 
6 660S 
4 650SX ( 9 623L+ 9 624L+ 9? 616L 
9 663S 
Matings 7 
~ Offspring 4S-6L 
Offspring (1918 crop) 
As the character of the matings 
again represented a back cross of 
simplex x recessive the result was 
quite similar as, in the preceding 
year, and in fact the two seasons’ crop, 
gave exactly the theoretical propor- 
tion to be expected from such a cross, 
namely, 9S + 9L. 
The following year, No. 650 was 
bred to four ewes only. Three of these 
(486, 501, and 550), being pure reces- 
sives, dropped four offspring, two 
short and two long eared lambs, which 
again maintained the proportions of a 
simplex x recessive cross. 
SIMPLEX CHARACTER ESTABLISHED 
Out of a total of 32 offspring (in- 
cluding two out of No. 127 not shown in 
diagram) derived from a simplex x 
recessive cross, 16 were short ear and 
16 long ear. This remarkable agree- 
ment of results obtained actually with 
results expected theoretically estab- 
lishes beyond doubt the simplex char- 
acter. 
The interesting feature, however, 
developed from the mating between 
this simplex ram and ewe No. 651 
3 Correns, C. 1912, Die Neuen Vererbungsgesetze. 
4 Bateson, W. 1909. 
5 Hurst, C.C. Experiments with Poultry. 
p. 283. 
Xxix. 
9° 664L+ 6 665L+ 6 666L 
9 667L J 
which was also a simplex, correspond- 
ing, therefore, to a mating inter se of 
F, the result being a ram lamb No. 
698 which had no ears. 
EARLESS TYPE A PURE DOMINANT 
Only four offspring from simplex x 
simplex matings. had been obtained 
before and these gave the proportion 
3S:1L. While the short ear was 
formerly accepted as the somatic 
expression of the pure dominant and of 
the heterozygote, assuming complete 
dominance, it now seems clear that the 
pure dominant is somatically earless 
and the heterozygote, showing only 
imperfect dominance, is short eared. 
In other words, if a single dose for 
repressing ear length is present the 
ear is approximately half normal 
length but if two such doses come 
together the ear is entirely eliminated. 
In this we have a clear-cut case of a 
heterozygous combination that can be 
easily distinguished from the homozy- 
gous dominants and recessives, and it 
forms a rather striking example of the 
“presence and absence hypothesis’’ 
of Correns,* Bateson,’ and Hurst.® 
Gebruder Borntraeger, Berlin. 
Mendel's Law of Heredity. Cambridge University Press, Cambridge. 
s Rep. Evol. Committee Roy. Soc. 1905, II. p. 131. 
§ Hurst, C. C. Experimental Studies on Heredity in Rabbits. 
Linn. Soc. Journ. Zool. 1905, 
