ins 



THE AMEUICA.X XA TURAL1SJ 



[Vol. LIV 



be able to escape detection by breeders unless the most careful 

 individual records were kept. However, non-disjunction in the 

 female fails entirely to account for the occurrence of the ob- 

 served exceptions in the reciprocal cross and may for that reason 

 be disregarded. 



Instead, therefore, of increasing the probability that non-dis- 

 junction is involved in the production of the exceptions noted, a 

 consideration of the above cross shows that it either fails to ac- 

 count for the exceptions which do occur or else expects additional 

 color classes which have not been observed. 



2. Canaries: 



Here the conditions differ but slightly from those already de- 

 scribed for doves. The factors involved are P, dark eye color 

 epistatic to p, pink eye color. P is commonly considered as sex 

 linked. The possibilities of non-disjunction remain the same as 

 in doves and may. therefore, be taken up under parallel headings. 



Cross of Pink-eyed Male X Dark-eyed Female. 



forming gametes ppFFMM and — PPM and 



(c) If non-disjunction in the female : 



forming gametes pFM PpFFMm 



It is in this cross that exceptional dark-eyed female; 

 (&) Non-disjunction in the male: 



(1) PppFFFMMM — pr. 



(2) PFM — =dai 



(3) pppFFFMMm =pin 



