78 INHERITANCE IN POULTRY. 



BODY LACING. 



This character is not found in the Jungle fowl, but may have been derived 

 from the penciling of the Aseel-Malay group. In male hybrids between 

 the Tosa fowl and the Dark Brahma it occurs, derived from the latter (p. 54). 

 It appears to be dominant. 



PENCILING. 



This is an ancient feminine characteristic, best marked in the Aseel- Indian 

 group (p. 53). It is found particularly well developed in the Dark Brahma 

 female. In the female hybrids between that race and the Tosa fowl penciling 

 is well developed ; it is dominant. 



GENERAL TOPICS IN INHERITANCE. 



UNIT CHARACTERS. 



Taxonomic descriptions of plants and animals give a list of their specific 

 characteristics (Merkmale, caracteres). These comprise for the most part 

 only the external characteristics, but a similar list might be made for internal 

 characteristics. In addition to specific characteristics, those of a higher 

 order (such as generic, etc.) and those of a lower order (such as varietal) may 

 be enumerated. Such characteristics are, in first approximation, unit char- 

 acters. They are of prime importance, because the whole problem of evolution 

 is that of the origin and significance of the various unit characters of the 

 body. 



The theory of the unit character is associated with that of its bearer in 

 inheritance. Darwin (1876) and later de Vries (1889) designated as such 

 bearers particles of the nuclear material named " pangenes." "Changed 

 numerical relation of pangenes is the basis of fluctuating variability ; dis- 

 placement (Umlagerung) of pangenes in the nucleus conditions retrogressive 

 and degressive mutations ; while the formation of new kinds of pangenes is 

 necessary to the explanation of progressive mutations ' ' (i. c. , those exhibit- 

 ing altogether new characteristics). 



The two main hypotheses of the origin of unit character ire that of de Vries 

 and that of Weismann. De Vries sets forth his hypothesis at the very begin- 

 ning of his great work, " Die Mutationstheorie. " His words may be thus 

 translated : 



As mutation theory I designate the doctrine that the characteristics of organisms are 

 built up of units that are sharply separable one from another. These units can be united 

 into groups, and in related species the same units and groups recur. Transitions, such 

 as the external forms of plants and animals exhibit in such numbers, exist between the 



units as little as between the molecules of chemistry In the realm of the doctrine 



of descent this principle leads to the conviction that species have proceeded from one 

 another not continuously but by steps [nicht fliessend, aber stufetiweise]. Each new unit 

 added to the older ones constitutes a step and separates the new form, as an independent 



species, sharply and fully from the species whence it arose Die neue Art ist somit 



mit eiuetn Male da ; sie entsteht aus der friiheren ohne sichtbare Vorbereitung, ohne 

 Ubergange. 



