No. 50D] Till-: < A TKdOh'IES OF YARIAIK) 



not seem to be an invariable occurrence. Davenport has 

 shown that albinism in poultry is in sonic cases a non- 

 Mendelian character, and the same is probably true, ac- 

 cording to Castle, for the lop-eared condition in rabbits. 

 In the inheritance of long and short hair in guinea pigs 

 there is also a marked departure from Mendelian ratios. 

 In silkworms Kellogg has shown that while most features 

 are Mendelian, cocoon color in some cases follows Men- 

 delian ratios, but in others it proved to be "inconstant 

 as to dominance and recessiveness and numerical propor- 

 tions, and may even break down and blend." Deaf 

 mutism also refuses to come under Mendelian categories 

 according to the statistics compiled by Bell. The fore- 

 going are cases of apparent retrograde variations which 

 form an exception to Mendel's law, but it must be ad- 

 mitted that the majority of such variations which have 

 been investigated show a fair approximation to Men- 

 delian ratios. 



In the crosses between the elementary species ot 

 (Luothna lamurckmna there is commonly a splitting 

 up in the first generation with absence of splitting in the 

 second and subsequent ones. Hybrids of 0. Lamm > ,i<nni 

 and 0. biennis, however, have nearly the aspect of the 

 latter species and remain true in the second and su (se- 

 quent generations without reversion or splitting. i <>ss< s 

 between 0. muricata and 0. hirtelhi produced hybrids 

 showing the characters of both parents. Ih< ^'J' 

 progagated through four generation- and remains inn 

 to this type, showing only slight fluctuations and nevei 

 reverting or segregating the mixed characters. n 

 stances of constant hybrids between different s j )0< ' H '^ 

 very common and it is unnecessary to specify thein m-h-. 

 Such constancy according to I)e Vnes is ^ ° ne ^ distinct 



elementary species m \ 

 pangen. 



The attempt to make 



the by 



