INHERITANCE OF FECUNDITY 155 



'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 character 

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



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

 dity 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 

 fowls with 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 approximation to the solution 

 of the problem has now been reached. While there remain ob- 

 scure 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 men- 

 tioned. In doing this it will be necessary to bring forward evi- 

 dence of several distinct sorts, anatomical and physiological as 

 well as genetic. Only by approaching this problem of the inher- 

 itance of fecundity from all angles has it been possible to gain that 

 understanding of the character itself which, in this instance 

 certainly, is absolutely essential to a correct interpretation of 

 any results respecting its inheritance. 



BIOLOGICAL ANALYSIS OF 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 follows, 

 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 inclividual organism, 

 as denoted by its ability to form and separate from the body mature 

 germ cells. "Fecundity in the female will depend upon the production 

 of ova and in the male upon the production of spermatozoa. In mam- 



