158 RAYMOND PEARL 



even often be met. Further, as has been especially emphasized by 

 Herrick (18, 19, and other papers), egg laying in wild birds is 

 simply one phase of a cyclical process. If the cycle is not dis- 

 turbed in any way the egg production is simply the minimum 

 required for the perpetuation of the race. If, however, the cycle 

 is disturbed, as for example, by the eggs being removed from the 

 nest as fast as they are laid, a very considerable increase in the 

 total number of eggs produced will result. This, of course, is 

 what happens under domestication. What an effect in increas- 

 ing the actual expressed fecundity of a wild bird the simple re- 

 moval of eggs as fast as they are laid may have, may be illustrated 

 by three cases from the literature. Austin (1) shows that whereas 

 the wild Mallard duck in a state of nature lays only 12 to 18 eggs 

 in the year, it will lay from 80 to 100 if they are removed as fast 

 as laid and the bird is kept confined in a pen at night. Hanke 

 (16) by regularly removing the eggs got 48 in succession from a 

 common wryneck (Inyx torquilla^). Wenzel (53) in the same 

 way brought a house sparrow's productivity up to 51 eggs. 



With the domesticated Gallus the 'normal ovulation' factor 

 may be taken as inducing a production of anything up to from 

 forty to eighty eggs in a year, this production being spread over 

 the period of from sometime in February to September or Octo- 

 ber. In this physiological complex are involved the elaboration 

 and deposition of yolks, the rapid growth of a few oocytes just 

 preceding ovulation, ovulation itself, the activation of the oviduct, 

 etc. The details of some of the processes involved have been 

 described elsewhere (cf. Rubaschkin (44), Sonnenbrodt (48), 

 Pearl and Curtis (33) and Pearl and Surface (37)) and do not 

 concern us here. The essential point to be noted is that in this 

 normal ovulation factor we are dealing with the basic physiological 

 processes of normal 'unimproved' laying. To make a normal lay- 

 ing hen it is necessary to have present both the anatomical basis 



' I give this scientific name with much hesitation, not knowing what pranks the 

 rule of priority or other nomenclatorial disturbers of the peace may have played 

 with it. in recent years. In any event the common name will quite sufficiently 

 indicate what bird it is that is here imder discussion. 



