164 RAYMOND PEARL 



more perfect metabolism, including the distribution of substance 

 and energy to the ovary, on which very heavy demands are laid in 

 a high fecundity record. Immediately it involves a control of 

 the process by which the supply of oocytes on the ovary in the 

 final stages of rapid growth by yolk deposition is kept at a rela- 

 tively high level for long periods of time. Sonnenbrodt's (48) 

 work suggests that the interstitial cells of the ovary may be 

 connected with the process. Thus he says (loc, cit., p. 421): 

 ''Bei alteren Hiihnern findet man die Zwischenzellen immer 

 noch, und besonders in der Nahe der Gefasse. Sie liegen heir 

 gruppen-und nesterweise zwischen den Follikeln und vor allem 

 auch in den Stielen der grosseren Follikel,^ immer dort, wo beson- 

 ders starke Blutzufuhr giinstige Ernahrungsbedingungen bietet." 



It is quite conceivable that the presence of numerous inter- 

 stitial cells on the stalks of the follicles of rapidly growing oocytes 

 is a cause of the rapid growth rather than an effect, as Sonnen- 

 brodt suggests. The whole subject of the intimate physiology 

 of the ovary needs more study. 



Whatever the precise nature of the factor under discussion, which 

 is a matter for future investigation, the main points which appear 

 clear at present are that: (a) high fecundity represents a defi- 

 nite addition to the normal egg production sufficient in amount for 

 purposes of reproduction. This added fecundity has been shown 

 (cf. 2S, 30) to be definitely inherited in certain cases at least and 

 may be regarded as dependent on or determined by some physio- 

 logical factor or complex of factors not present in birds which 

 exhibit a low degree of fecundity.-^ This physiological complex 

 may be designated as the 'excess production' factor in fecundity. 



We may next consider in greater detail these factors influencing 

 fecundity^ taking first 



^ My italics.— R. P. 



* Throughout this discussion it is presumed that the reader will understand with- 

 out repeated specific statements that attention was paid to environmental factors 

 in the experimental work. That is, when the statement is made that one bird or 

 set of birds exhibits high fecundity and another low fecundity it is to be understood 

 that both sets were hatched, reared, fed and cared for in all respects in as nearly 

 precisely the same way as is possible, considering that fowls are, in some degree, 

 free agents and cannot be absolutely controlled. The extent both in time and 



