COMB-LOP.
In races having a large single comb this is usually erect in the
male, but in the female lops over to the right or left side of the
head. This lop is determined before hatching; indeed, in the male it
may be ascertainable only in the embryo or in the recently hatched
chick. The position of the comb is permanent throughout the life of
the pullet and hen and, if pressed to the opposite side, it quickly
returns to its original position. At one time I entertained the
hypothesis that its position was determined by the pressure of the
foot against the head while the chick was still within the shell; but
after finding the comb lying both to the right and to the left when
in contact with the foot I abandoned this hypothesis as untenable. It
seemed possible that this position is hereditary, and so data were
collected to test this hypothesis. It is not always easy to decide
definitely, even for the female, as to the direction of the lop; for
the anterior part of the comb may lop to the right, the posterior
part to the left, or _vice versa_. In that case one selects the
larger or better defined lopping portion to designate as _the_ lop.
This is usually the posterior portion of the comb. However, such
doubtful cases may be omitted from consideration here, as there are
plenty of examples of well-defined lop on both sides of the head.
TABLE 56.
+------------------------------------------------------+
| Both parents with right lop. |
+----------+-----------+-----------+-------------------+
| | | | Offspring. |
| Pen No. | No. of | No. of +---------+---------+
| | mother. | father. | Right. | Left. |
+----------+-----------+-----------+---------+---------+
| | | | | |
| 817 | 6188 | 3900 | 7 | 8 |
| 817 | 6406 | 3900 | 12 | 17 |
| 831 | 1011 | 4213 | 7 | 16 |
| 831 | 3040 | 4213 | 13 | 10 |
| 831 | 4219 | 4213 | 4 | 21 |
| 831 | 6602 | 4213 | 6 | 15 |
| 833 | 1310 | 4222 | 4 | 7 |
| 833 | 4361 | 4222 | 6 | 4 |
| 833 | 7519 | 4222 | 2 | 4 |
| 904 | 4714 | 7870 | 6 | 7 |
| | | +---------+---------+
| | | | 67 | 109 |
+----------+-----------+-----------+---------+---------+
| Both parents with left lop. |
+----------+-----------+-----------+---------+---------+
| | | | | |
| 841 | 3867 | 3890 | 3 | 9 |
| 841 | 4663 | 3890 | 9 | 7 |
| 903 | 9824 | 8463 | 6 | 5 |
| | | +---------+---------+
| | | | 18 | 21 |
+----------+-----------+-----------+---------+---------+
| Mother left lop, father right. |
+----------+-----------+-----------+---------+---------+
| | | | | |
| 831 | 1980 | 4213 | 9 | 17 |
| 904 | 3901 | 7840 | 4 | 3 |
| 904 | 7645 | 7840 | 6 | 3 |
| | | +---------+---------+
| | | | 19 | 23 |
+----------+-----------+-----------+---------+---------+
| Mother right lop, father left. |
+----------+-----------+-----------+---------+---------+
| 903 | 3946 | 8463 | 2 | 0 |
| 903 | 4079 | 8463 | 7 | 2 |
| 903 | 4082 | 8463 | 11 | 6 |
| | | +---------+---------+
| | | | 20 | 8 |
+------------------------------------------------------+
| Summary. |
+-----------------------------+------------------------+
| | Offspring. |
| Parents. +------+--------+--------+
| |Total.| Right. | Left. |
+-----------------------------+------+--------+--------+
| | |_P. ct._|_P. ct._|
|Both with right lop | 176 | 38 | 62 |
|Both with left lop | 39 | 46 | 54 |
|Mother left lop, father right| 42 | 45 | 55 |
|Mother right lop, father left| 28 | 71 | 29 |
+-----------------------------+------+--------+--------+
From table 56 it appears, summing all cases, that there are more
left-lopping offspring than right-lopping as 161 to 124 or as 56.5
per cent to 43.5 per cent and that this excess holds whether both
parents are right-lopping, or both left-lopping, or the mother
left and the father right. Only in the case when the mother is
right-lopping is there a majority of offspring of the same sort,
but here the numbers are too inconsiderable to carry much weight.
Although there is not clear evidence of any sort of inheritance,
it is probable that the position of the lop is not determined by a
single factor, but by a complex of factors.
The conclusion that right and left conditions are not simple,
alternative qualities accords with the results obtained by others.
Thus Larrabee (1906) finds that the dimorphism of the optic chiasma
of fishes (in some cases the right optic nerve being dorsal and in
others the left) is not at all inherited, but in each generation the
result is strictly due to chance. This is, perhaps, the same as my
conclusion that the hereditary factors are complex. Lutz (1908) finds
that in the mode of clasping the hands interdigitally the right thumb
is uppermost in 73 per cent of the offspring when both parents clasp
with right thumb uppermost, but in only 42 per cent of the offspring
when both parents clasp with left thumb uppermost. The mode of
clasping is inherited, but not in simple Mendelian fashion.