| |----|----|----| | Totals (189) | 95 | 95 | 4 | | Percentages |49.0|49.0| 2.0| +-----------------------------------------------------+----+----+----+ The mating of extracted I comb and Y comb, both of the second (or later) hybrid generation, gives the following distribution of types in the offspring (table 6): Y comb 95 (49 per cent); I comb 95 (49 per cent); oo comb 4 (2 per cent). In detail the results given in table 6 accord badly with the second hypothesis, which demands some families with 100 per cent Y comb. The mating of extracted oo comb×Y comb, where both parents are of the second hybrid generation, gave the distribution of comb types in the 6 families that are recorded in table 7. TABLE 7. +---+-----------------+-------------------------+ | | Parents. | Offspring. | |Pen|-----------------+-----+-----+-----+-------| |No.| ♀ | ♂ | I | Y | oo |Absent.| | | (F2). | (F2). | | | | | +------------+--------|-----+-----|-----|-------| |634| { 298 | 444 | 0 | 15 | 18 | .... | | | { 366 | 444 | 5 | 23 | 15 | .... | | | | | | | | | |729| { 913 | 936 | 2 | 28 | 37 | .... | | | { 935 | 936 | ....| 13 | 39 | .... | | | | | | | | | |756| { 1043 | 1390 | ....| 13 | 11 | 1 | | | { 1048 | 1390 | ....| 0 | 5 | .... | | |-----+-----+-----+-------+ | Totals (214) | 7 | 92 | 115 | 1 | +---------------------+-----+-----+-----+-------+ The single comb recorded in the case of 7 birds is doubtless merely the limiting condition of a Y comb in which the median element is developed to its fullest extent. All but 2 of the 7 were recorded from early embryos when an incipient bifurcation would be more difficult to detect. This explanation applies generally, and accounts for the usual excess of I comb when compared with Y comb, as for instance in table 3, page 7. Returning to table 7, it is, consequently, probable that only the Y-combed and non-median-combed offspring are produced and that they are in the proportion of 99 to 115 or of 46 per cent to 54 per cent. If we add together all records of a oo×Y cross, disregarding the generation of the parents, we get a total I comb 5,[1] Y comb 177, oo comb 172, and absent 3, or 182 (51 per cent) with the median element and 175 (49 per cent) without. Thus the oo×Y cross gives the 1:1 proportion called for on the first and third hypotheses and not at all the variety required by the second hypothesis. [1] Excluding 6 doubtful because from too young embryos and not observed by myself. TABLE 8.