116 MASS. EXPERIMENT STATION BULLETIN 199. 



Summary and Conclusions. 



The working hypothesis is adopted that — 



1. Broodiness depends upon the presence of a "complete mechanism" 

 in the individual, from which it follows that the absence of broodiness 

 depends upon the loss of some essential part of this mechanism, or upon 

 its inhibition by some secondarj'' factor. 



2. The inheritance of broodiness may be expected to vary from flock 

 to flock. 



3. In the flocks studied, non-broodiness appears to result from the loss 

 of one or both of two genes from the complete germinal complex, while 

 there is some evidence that a dominant inhibitor may also exist in the 

 germ plasm of these flocks. 



4. By suitable breeding methods it has been possible to develop quickly 

 a strain of low degree of broodiness from a strain with a very high degree 

 of broodiness. 



, 5. Statistical constants for certain broody characters are given. 



Literature Cited. 



Bateson, W., 1902. Experiments with Poultry. Reports to the Evolution Com- 

 mittee of the Royal Society. Report I, pp. 87-124. 



Gerhartz, H., 1904. Ueber die zum Aufbau der Eizelle Notwendige Energie. 

 (Transformationsenergie) Pfluger's Arch. Bd. 56, pp. 1-224. 



Goodale, H. D., 1918. Internal Factors influencing Egg Production in the Rhode 

 Island Red Breed of Domestic Fowl. Am. Nat, Vol. LII, pp. 65-94, 209-232, 

 301-321. 



Herrick, F. H., 1907a. Analysis of the Cyclical Instincts of Birds. Science, N. S., 

 Vol. XXV, pp. 725, 726. 



, 19076. The Blending and Overlap of Instincts. Science, N. S., Vol. XXV, 



pp. 781, 782. 



Hurst, C. C, 1905. Experiments with Poultry. Reports to the Evolution Com- 

 mittee of the Royal Society. Report II, pp. 131-154. 



Kirkpatrick, W. F., and Card, L. E., 1917. Fifth Annual International Egg-laying 

 Contest. Bulletin No. 89, Storrs Agricultural Experiment Station, pp. 257- 

 301. 



Pearl, R., 1914. Studies on the Physiology of Reproduction in the Domestic Fowl. 

 VII. Data regarding the Brooding Instinct in its Relation to Egg Production. 

 Journal An. Beh., Vol. 4, pp. 206-288. 



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