CHARACTERISTICS IN HYBRIDS. 21 



that there is a reversion in some characters to the serin or Girlitz 

 {Serinus hortulanus Koch), probably close to the ancestor of the wild 

 canary. These characters are four: "in der breiten Binde der Spitzen 

 der Armschwingen, den Fliigelbinden der Deckfedern, den Farbung 

 der Schultern, den Saumen der Steuerfedern." But in respect to the 

 first and last of these characters I find in my birds no important differ- 

 ence from the green canary, except a slight yellowing of the lighter 

 areas. The color of the shoulders of the hybrid is, as it were, the 

 sum of the colors of the goldfinch and the canary. As to the second 

 of the differential characters — the yellow wing-bow — this is highly 

 variable in my hybrids and in mottled canaries. We have no reason to 

 conclude that there is reversion to the serin, and it is undesirable to 

 rest with so vague a term as reversion as an "explanation" of the 

 resemblance of the hybrid to the "green canary." 



But if not reversion, under what rubric shall we place the greenness 

 of the goldfinch X canary hybrid ? First it is to be recalled that the 

 yellow canary is a green deprived of black pigment. When black pig- 

 ment is added from any source it occupies the emptied spaces and so 

 restores the "green" andtheblack. Consequently we find streaking 

 on the sides of the body in the goldfinch-canary hybrid and black on 

 tail and wings. But the canary contains also a mottling factor and so 

 the hybrid is "green" in certain areas only. The other areas are 

 yellow or else yellow to which the chocolate color has been added on 

 the back, wing coverts, and sides, and to which red has been added on 

 the face. The belly, which is white in the goldfinch, remains yellow 

 in the hybrid. 



How, then, shall we conceive the gametic formula of the gold- 

 finch and the yellow canary ? As the goldfinch contains black (TV^), 

 red, and chocolate, its formula may be given as N, R, C, m, while that 

 of the canary is n, r, c, M, contributing only the mottling character. 

 Then the zygote gives NRCMas dominants, and the adult hybrid shows, 

 on top of the yellow, black, red on the face and chocolate on the back 

 and the sides. 



The foregoing theory of the gametic constitution of the yellow 

 helps, moreover, to explain the great variability of the hybrids — corre- 

 sponding to the variability of the mottled offspring of yellow X green. 

 As we have seen that in an extreme case the hybrid yellow X green is 

 practically yellow, so likewise the hybrid yellow X goldfinch is occa- 

 sionally, though rarely, entirely or almost entirely yellow except for 

 the red on the face. 



Finally, attention must be called to the principle of localization of 

 unit-characters. Red is found almost invariably in the goldfinch 

 hybrid, but always confined to the head region. Chocolate occurs in 



