582 REPORT—1904. 
One very important group of cases exists, in which the appearance of a partial 
failure of segregation after the second generation (F’,) is really due to another 
phenomenon. The visible character of a zygote may, for instance, depend on 
the coexistence in it of two characters belonging to distinct allelomorphic pairs, 
each capable of being independently segregated from its fellow, and forming 
independent combinations. For the demonstration of this important fact we are 
especially indebted to Cuénot.1_ We have indications of the existence of such a 
phenomenon in a considerable range of instances (mice, rabbits (Hurst), probably 
stocks and sweet peas). 
Nevertheless, there are other cases, not always easy to distinguish from these, 
where some of the gametes of F, certainly carry on heterozygous characters 
unsegregated. As an example, which seems to me indisputable, I may mention the 
so-called‘ walnut’ comb, normal to Malay fowls. This can be made artificially 
by crossing rose-comb with pea-comb, and the crossbred then forms gametes, of 
which one in four bears the compound unsegregated.* We may speak of this as a 
true synthesis. 
In another type of cases segregation occurs, but is not sharp. The gametes 
may then represent a full series ranging from the one pure form to the other, 
Such cases occur in regard to some colours of Primula sinensis, and the leg- 
feathering of fowls (Hurst). In the second generation a nearly complete series of 
intermediate zygotes may result, though the two pure extremes (if the case be one 
of blending characters) may still be found to be pure. 
Resolution and Disintegration.—Besides these cases, the features of which we 
now in great measure comprehend, we encounter frequently a more complex 
segregation, imperfectly understood, by which gametes of new types, sometimes 
very numerous, are produced by the crossbred. Each of these new types has its 
own peculiarities. We shall, I think, be compelled to regard these phenomena as 
produced either by a resolution of compound characters introduced by one or 
both parents, or by some process of disintegration, effected by a breaking-up of 
the integral characters followed by recombinations. It seems impossible to 
imagine simple recombinations of pre-existing characters as adequate to produce 
many of these phenomena, Such a view would involve the supposition that the 
number of characters pre-existing as units was practically infinite—a difficulty 
that as yet we are not obliged to face. However that may be, we have the fact 
that resolutions and disintegrations of this kind—or recombinations, if that con- 
ception be preferred—are among the common phenomena following crossing, and 
are the sources of most of the breeder’s novelties. As bearing on the theoretical 
question to which I have alluded, we may notice that it is among examples of 
this complex breaking-up that a great proportion of the cases of partial sterility 
have been seen. 
No quite satisfactory proof as to the actual moment of segregation yet exists, 
nor have we any evidence that all characters are segregated at the same cell- 
division. Correns has shown that in maize the segregation of the starch character 
from the sugar character must happen before the division forming the two genera- 
tive nuclei, for both bear the same character. The reduction-division has naturally 
been suggested as the critical moment. The most serious difficulty in accepting this 
1 When abc... xaBy... gives in F, or F,a character (not seen in the original 
parents), which from F, or later may breed true: not because aa, 6B, cy do not 
severally segregate, but through simultaneous homozygosis of, say, aa and B8, giving 
a zygote aaBBcy . . . which will breed true to the character af. 
? Owing to this behaviour, and to the simultaneous production of single-comb 
(? by resolution), there are,even in pure Malays, five types of individuals, all with 
‘walnut’ combs—as yet indistinguishable—formed by gametic unions 7 x p, mp x rp, 
ry x7, 7p xp,rpxs. Of these kinds three can at once be distinguished by crossing 
with single; but whether 7 x p can be distinguished from 7p x s we do not yet know 
[7, rose; p, pea; s, single; 7p, walnut.] In this example four allelomorphs are 
simultaneously segregated, one being compound. Neglecting sexual differentiation, 
there are therefore ten gametically distinct types theoretically possible; but of these 
only four are distinguishable by inspection, ove 
