PHYSIOLOGY OF REPRODUCTION IN DOMESTIC FOWL. 59 



It might also be repeated here that the three triple-yolked 

 eggs were all produced by pullets less than six months old. 



The third observation is that only normal single-yolked eggs 

 were produced by three pullets which did not lay until they 

 were 8% to 9 months of age. Every egg of these birds was 

 opened. Since 80 per cent, of the pullets between 5 and 7 

 months of age lay only normal single-yolked eggs, this third 

 observation has no statistical value, but it is given since it is 

 the only absolutely accurate data at present available on the 

 eggs of the birds which begin to lay when fully mature. 



The kind of disturbances which result in the formation of 

 double- and triple-yolked eggs are not yet thoroughly understood. 

 From the preceding paragraphs it would appear that whatever 

 their nature they are more apt to occur in immature than in 

 mature birds. Yet during six years observation, the Experiment 

 Station's flock, consisting each year of from 600 to 800 birds, 

 has produced double-yolked eggs during every month of the 

 year. This accords with Immerman's observations in Basel 

 and indicates that such disturbances may occur at any time. 



Parker quotes Landois' 1 statement that the laying of double- 

 yolked eggs may become habitual with certain hens and also 

 cites the single cases of such birds noted by Bartels 2 and Immer- 

 man. 3 A third single case has since been reported by Glaser. 4 



Not a single case of this kind has occurred among the large 

 number of birds owned by this station during the last six years. 

 This fact together with the small number of the actual cases cited 

 in the literature indicates that birds which habitually lay double- 

 yolked eggs are very rare. The occasional occurrence of such 

 cases, hcwever, indicates that physiological disturbances capable 

 of causing such a result may become chronic. 



Data from the station flock, however, indicate that even when 

 the disturbances are not chronic they may recur several times 

 in one individual, i. e., an individual may show a predisposition 



1 Landois, "Missbildungen bei Hiinner-Eiern," Zoo/. Garten, Jahrg. 19, pp. 17-24 



2 Bartels, M., "Hiihner Ei mit Zwei Dottern," Sitzungs-Ber. Gesellsch. naturf 

 Freunde Berlin, Jahrg. 1895, pp. 143-145. 



3 Immerman, loc. cit. 



4 Glaser, O., "The Origin of Double- Yolked Eggs," BIOL. BULL., Vol. XXIV., 

 pp. 1 75-18^- 



