INHERITANCE OF FECUNDITY IN DOMESTIC EOWE. 285 



Second: that, notwithstan'ding the fact just mentioned, fecun- 

 dity is, in some manner or other, inherited in the domestic fowl. 

 This must clearly be so, to mention but a single reason, because 

 it has been possible to isolate and propagate from a mixed flock 

 'pedigree lines' or strains of birds which breed true, generation 

 after generation, to definite degrees of fecundity. Some of 

 these lines breed true to a high condition or degree of the char- 

 acter fecundity ; others to a low state or degree of this character. 



Definite as these results are they give no clue as to how 

 fecundity is inherited; what the mechanism is. Plate (43) has 

 recently said: "Das Ziel ,der Erblichkeitsforschung muss die 

 Aufstellung von 'Erbformeln' fiir alle untersuchten Merkmale 

 sein." This expresses the case precisely. To determine the 

 'Erbformeln' of fovvds v/ith respect to fecundity has been the 

 goal towards which every part of the present investigation has 

 been directed and urged. It is believed that a first approxima- 

 tion to the solution of the problem has now been reached. 

 W'hile there remain obscure points still to be cleared up, yet 

 the results now in hand appear to indicate pretty clearly the 

 general character of the mechanism of the inheritance of 

 fecundity, and to show what lines further investigation of the 

 problem may most profitably take. It is the purpose of this 

 paper to present an account of the results mentioned. In doing 

 this it will be necessary to bring forward evidence of several 

 distinct sorts, anatomical and physiological as well as genetic. 

 Only by approaching this problem of the inheritance of fecund- 

 ity from all angles has it been possible to gain that understand- 

 ing of the character itself which, in this instance certainly, is 

 absolutely essential to a correct interpretation of any results 

 respecting its inheritance. 



BIOEOGICAL ANALYSIS OE THE CHARACTER FECUNDITY 



At the outstart it will be well to understand clearly what is 

 meant by the term -fecundity as here used. In a former paper 

 (34) the terms 'fecundity' and 'fertility' were defined as fol- 

 lows, and have been used as there defined throughout the course 

 of the investigation : 



We would suggest that the term 'fecundity' be used only to 

 designate the innate potential reproductive capacity of the in- 

 dividual organism, as denoted by its ability to form and sepa- 



