172 RAYMOND PEARL 



a century and a quarter ago regarding the cuckoo is of interest. 

 He says: 



That the cuckow actually lays a great number of eggs, dissection 

 seems to prove very decisively. Upon a comparison I had an oppor- 

 tunity of making between the qvarium, or racemus vitellorum, of a 

 female cuckow, killed just as she had begun to lay, and of a pullet killed 

 in the same state, no essential difference appeared.^ The uterus of each 

 contained an egg perfectly formed and ready for exclusion; and the 

 ovarium exhibited a large cluster of eggs, gradually advanced from a 

 very diminutive size to the greatest the yolk acquires before it is received 

 into the oviduct. 



The viechanism of the inheritance of fecundity 



With so much by way of introduction we may proceed to the 

 subject in hand, namely a detailed account of the manner in 

 which fecundity is inherited. In this account for reasons which 

 have been stated above, and in earlier papers on this subject, 

 attention will be confined to winter egg production. 



A . Observed types of winter egg production. A study of numer- 

 ous statistics shows that hens fall into three well defined classes 

 in respect to winter production. These classes include (a) those 

 birds which lay no eggs whatever in the winter period (up to 

 March 1 of the laying year) ; (6) those that lay but have a produc- 

 tion during the period of something under about 30 eggs; and 

 finally (c) those whose production exceeds 30 eggs in the winter 

 period. The division point between classes (6) and (c) is not 

 sharply defined in every case, but it is plainly (as will appear 

 later) at about 30 eggs. Since in the analysis some fixed point 

 must be taken for this boundary a production of 30 has been 

 chosen for this purpose and will be used throughout. This is an. 

 arbitrary choice only in the sense that it is a convenient round 

 number lying near where the biological division point falls, at 

 least in the strains of domestic fowls used in these experiments. 

 The analysis could doubtless be carried through nearly or quite 

 as well by taking the division point at a production of 29 or,31, 

 but 30 is a more convenient figure. 



' Italics not in original. 



