EMBRYOLOGY 



75 



Annual Changes in Egg Quality 



So far, only the changes in various physical and chemical properties of the eggshell have 

 been determined. Data for the composition of the egg contents are not sufficient to warrant 

 reporting. 



It was established that there are differences in shell quality, year by year and. during any 

 one season, between clutches and even between eggs in a dutch. For example, figure 5 

 shows annual variations in eggshell thickness for the five-year period of the study, the year- 

 ly averages for each clutch and the different thickness of each eggshell. The average thick- 

 ness during 1936 and 1940 was higher than fur the intervening years. Yet each year had 

 some clutches with high and others with low averages, while individual eggs varied greatly. 



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1936 



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1937 







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. . • INDIVIDUAL VALUES 

 O AVERAGE PER CLUTCH 



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1938 



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NDIVIDUAL CLUTCHES 



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1940 



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I 234 56789 10 II 



FIGURE 5. ANNUAL CHANGES IN SHELL THICKNESS OF GROUSE EGGS COLLECTED FROM THE 



ITHACA, NEW YORK. REGION — 1936-1940 



Since hatchabilily is consistently high, a change in eggshell thirkncss seems of little sig- 

 nificance. However, future study of thickness and composition of the shells of eggs which 

 had hatched, as compared with those in the clutch which did not. may give some new evidence 

 as to how these qualities influence hatching. Their effect on livability may also be determined 

 by checking tlicm against the sulisequent mortality of the chicks. More time and greater 

 numlters than have been availalile fur ibis study are required to make tlic data r<nulusive. 



