Allgemeine Biologie und Entwickelungslehre. 21 



lowing may be noted. While there is no doubt as to the existence of unit 

 characters in poultry, such characters" are not rigid and immutable but are 

 frequently changed in the process of hybridization. A character extracted after 

 a cross (c. g. : in extracted recessives) is usually found to have been altered in 

 the cross from its original pure condition. 22 characters out of those studied 

 were found to exhibit alternative inheritance in some degree. Three characters 

 show particulate inheritance. True blended inheritance between qualitatively 

 marked characters is probably rare. De Vries's law that specific and varietal 

 characters are inherited in different ways is not found to hold universally for 

 poultry. A patent character is in general domiuant over a latent character, 

 but there are exceptions. Phylogenetically old characters are, on the average, 

 not less likely to be dominant than new characters. Various exceptions to the 

 law of dominance were noted, principally that either dominance or recessiveness 

 may be incomplete. With certain exceptions , when one of a pair of allelo- 

 morphs is dominant it is always so regardless of the races crossed. A ten- 

 dency is noted towards a lack of complete reciprocity in reciprocal crosses with 

 regard to certain characters. There is some evidence that sexually dimorphic 

 characters in poultry can be transferred from one sex to the other. The normal 

 proportion of the sexes appears to be preserved in hybrids. Correlation of 

 characters is "only rarely due to physiological interdependence". "It is doubt- 

 less due to an accidental association of characters brought into the race by 

 successive mutations or by hybridizations and never disturbed, because not pre- 

 judicial to the well-being of the species". "Positive support for the mutation 

 theory is gained from a consideration of the characteristics of poultry". "The 

 very existence of unit characters is proof of the mutation theory". 



Bateson, Saunders & Punnett report on inheritance in various species of 

 plants and in Oallus. With respect to color characters in G. white is usually 

 found to be dominant to color, an exactly opposite relation to that usually 

 found in mammals. There exists however another class of white birds in 

 which the white behaves as a recessive to color. These recessive whites "are 

 characterized by the possession of a few minute ticks in their otherwise pure 

 white plumage". Detailed data are given regarding the inheritance of the 

 various comb types. 



Whitman discusses the evolution of the color patterns exhibited by the wings 

 of various species of Columba. Both observation and experiment (selection) 

 lead to the conclusion that evolution here has been primarily by a process of 

 orthogenesis. 



Castle( 1 ) presents data and discusses the inheritance of coat color in mice, 

 with special reference to the Mendelian theory of gametic purity. The results 

 in the main confirm Cuenot, The order of the dominance of the hair is yellow, 

 black, chocolate, each dominating the colors which follow it in the series and 

 being recessive to those which precede it. There are two types of yellow mice, 

 a "sooty-yellow" in which some chocolate pigment is associated with the yellow, 

 and a pure yellow type, in which yellow pigment alone is present. Both types 

 are probably heterozygous. The author criticises the "factor" theory of Cuenot 

 and Bateson, and concludes that it is more logical to consider that characters 

 may exist in varying states of activity. The presence of one character may 

 inhibit the activity of another, thus making it appear that the second is en- 

 tirely absent, though by proper breeding experiments it can be shown that this 

 cannot be the case. Thus if black and yellow are present together in mice 

 the activity of black is largely inhibited. Two such yellow mice bred together 

 may produce black offspring, proving that neither black nor any factor of black 



