200 



THE AMERICAN NATURALIST 



[Vol. XLVI 



ate. Second, it would appear that complete discontinuity 

 or entire dominance or recession are qualities in heredity 

 which may gradually evolve. Many characters show im- 

 perfect dominance (Castle, 1905) ; gametic purity is not 

 absolute (Castle, 1906) ; selection is of importance in the 

 improvement of races (Castle, 1907). There are a num- 

 ber of truly blending characters, such as lop-earedness 

 in rabbits (Castle, 1909), cross blends of long and short 

 hairs (Castle, 1906), cross blends between short- and lop- 

 eared rabbits which are permanent (Castle, 1909), blends 

 in weight inheritance and in skeletal proportion (Castle, 

 1909). 



More recent work has tended to show (Hatai, 1911) 17 

 that blended inheritance may be considered to be a lim- 

 ited case of alternative inheritance where dominance is 

 imperfect. Thus Mendel's law of alternative inheritance 

 may be considered as the standard in all the cases re- 

 ferred to it (Hatai, 1911, p. 106). Certain characters 

 which were considered formerly to blend are now re- 

 garded as showing a certain kind of segregation or unit 

 inheritance. Thus Davenport (1909) observes: 



Skin pigment does not show thorough blending inheritance, but segre- 

 gation (sometimes imperfect), a more pigmented being imperfectly 

 dominant over a less. is . . . The reason, the same author observes (1909, 

 for the blending of hair and skin color in man is the non-development 



Thus the prevalent recent opinion among Mendelian 

 observers is that there is a real discontinuity between the 

 germinal or Mastic characters and what the paleontol- 

 ogist or morphologist generally observes, is only an ap- 

 parent continuity between somatic characters. 



Ameb. Natoralist, Vol. XLV, Xo. 530, February. 1911, pp. 99-106. 

 intensity units, possibly one or a few large units, more probably a number 

 1910). 



