58 M. R. CURTIS AND RAYMOND PEARL 



'n' (nesting) record of such a bird is precisely like a normal egg record 

 showing the same phenomena of rhythm and cycles. Each day's 

 'n' in the record of such a bird represents an egg which she would have 

 laid, had she been physically capable of doing so. 



We have later shown (Pearl and Curtis '14) that in all cases 

 of surgical interference with the oviduct the ovary passes through 

 the same rhythm as in unoperated birds. In such cases the 

 formation of the egg proceeds as far as the obstruction to the 

 oviduct. 



The whole body of evidence is now so convincing that we can- 

 not escape the conclusion that nesting records are, in the great 

 majority of cases at least, associated with ovulation into the 

 body cavity, or the backing into it of a partly or fully formed egg. 



Patterson ('10) stated that "the stimulus which sets off the 

 mechanism for ovulation is not received until the time of lay- 

 ing (in cases where birds are laying daily) or shortly there- 

 after." He bases this assertion on the fact that before the 

 laying of the egg the oviduct is inactive, but ''shortly after 

 laying is in a state of high excitability with the infundibulum 

 usually clasping an ovum in the follicle." 



In view of the results set forth in No. VIII of these Studies, 

 and in the present paper, it would appear probable that the con- 

 nection, if there is any connection, between the instinct to nest 

 and to lay (i.e., to expel the completed egg) and ovulation is the 

 reverse of that implied by Patterson. Since birds which entirely 

 lack an oviduct (Pearl and Curtis '14) and therefore cannot by 

 any possibility lay an egg, still ovulate perfectly well and in a 

 normal rhythm, egg-laying cannot very well be the stimulus to 

 ovulation, as implied by Patterson. The explanation which 

 accords best with our present knowledge is that the instinct 

 to nest and to lay is the normal but not absolute (for example, 

 note that No. 364 was ovulating into the body cavity and not 

 nesting) resultant of ovulation, even in cases where the yolk 

 does not enter the oviduct. 



