THE BROODING INSTINCT IN THE DOMESTIC FOWL 285 



In the present state of knowledge the physiological cause or 

 basis of the phenomenon known as broodiness, which every 

 bird shows in one form or another, is not at all clear. From the 

 facts set forth in this paper it is obvious that broodiness is a 

 much more variable phenomenon than oestrus in mammals. 

 In the first place it lacks entirely the regularity of the occurrence 

 of oestrus. Even in the cases where periods of broodiness do 

 recur rather regularly (cf. Figs. 1,2, and 3) it is clear that we have 

 nothing like the regularity of the dioestrous cycle of mammals. 



It is furthermore certain that brooding is not a necessary or 

 essential element in the reproductive processes in the domestic 

 fowl, in the sense that any other element in the cycle is dependent 

 upon it as a necessary antecedent. Some hens which lay per- 

 fectly well throughout their lives, and whose eggs produce 

 perfectly normal healthy chickens never manifest the slightest 

 indication of the brooding instinct. 



It appears to be the case that in the domestic fowl the brooding 

 instinct has to a very large degree disappeared along with the 

 fact of domestication. This is particularly true in the case of 

 fowls which have been systematically bred for a considerable 

 period of time for high egg production. In such strains it is 

 difficult to find fowls in which the brooding instinct is sufficiently 

 strong to last out the 21 days necessary to hatch eggs. Here we 

 have repeatedly tried during the last six years to get broody 

 Barred Plymouth Rock hens to hatch eggs. Only in extremely 

 few cases has it been possible to do this. In most cases the bird 

 will sit for a while, then cease all manifestations of the instinct 

 and begin laying again. It seems highly probable that broodiness 

 is in some way dependent upon factors which are inherited in a 

 Mendelian manner. A large amount of material has been 

 accumulated regarding this point and it is hoped that the analysis 

 of it will soon be completed. 



It would seem that broodiness is rather directly connected 

 physiologically with the functioning of the ovary. That it is 

 not connected with the functioning of the oviduct is clearly 

 demonstrated in the present paper by the cases in which the 

 oviduct is removed, or put into a non-functioning condition. 

 In these cases, however, the normal functioning of the ovary 

 had in no wise been interfered with. It is an interesting fact 

 in this connection to note that birds in which the ovary is non- 



