74 THE SPECIES ITS TAXONOMY, RANGE. BIOLOGY, & ECONOMIC IMPORTANCE 



eggshell, and the thickness of shell membrane. All these, including the total ash and calcium 

 content of the eggshell, facilitate the functioning of the specific characteristic properties of 

 the egg of this species and are called its values. They are noticeably different in many respects 

 from those of the eggs of pheasant, quail and other domesticated birds'^. 



BLASTODERM 



ALLANTOIS 



ALBUMEN 



YOLK 



ALBUMEN 



YOLK SAC 



FRESH EGG ELEVEN DAY EMBRYO 



FIGURE 4. STRUCTURE OF THE FRESH AND OF THE DEVELOPING GROUSE EGG 



On the other hand, some of these values, when corrected for the size of the egg, show 

 striking similarities. The chemical composition of eggshell and possibly of egg contents, on a 

 percentage basis, are much the same as in the eggs of other species, especially of pheasant 

 and quail. The variation in relative values among individual eggs of the same species is fre- 

 quently greater than the variation between the averages for different species. 



There was little difference in physical properties and chemical composition between grouse 

 eggs from birds in the wild and from those in confinement. The eggs of wild birds had 

 somewhat stronger and tiiicker shells, with greater content of total ash and calcium. It 

 would seem from this that artificial environment and possibly the lack of natural foods have 

 modified the shell slrintiirc. There was a tendency for the eggs of captive birds to become pro- 

 gressively smaller, more elongated, and to have lliiriiirr. liiiiilcr. and more easily broken shells, 

 the later in the season ihev were laid. 



TABLE 8. 



PHYSICO-CIIHMICAL PKUl'KUTIKS OK CHOUSE EGGS COLLECTED KIlOiM 

 THE ITHACA, NEW YORK, REGION 19.S6-1910 



*ERg8 incubated a few days bcfora the time of delivery to the laboratory weighed somewhat leaa than they should at the 

 oorreapondinff period in the wild. 



