236 



THE UNFERTILISED EGG AS A 



[PT. Ill 



very susceptible to crushing and rough treatment. After boihng, the 

 spheres assume a polyhedral form. The granules seen within them must 

 consist of protein, for they are not soluble in ether or alcohol. On the 

 other handjthe white yolk elements are vesicles smaller than the globules 

 of the yellow yolk, being about 4 to 75 /n across, with a highly refractive 

 body, often as small as i [x, in the interior of each. These vesicles are 

 sometimes collected together into much larger vesicles. They observed 

 also underneath the blastoderm or the germinal disc a number of 

 large vacuoles filled with fluid — large enough, in fact, to be seen with 

 the naked eye. The histology of yolk has been reviewed by Dubuisson, 

 and at one time many papers were published on it, e.g. those of 

 Virchow. They cannot be considered in detail here. 



1-3. The Proportion of Parts in the Avian Egg 



Of the weight of the whole egg, the shell takes up about 10 per 

 cent., the albuminous white 50 per cent, and the yolk 30 per cent, 

 in round numbers. These relationships have been determined by a 

 multitude of investigators, whose results are drawn up in Table i . 



Table i . Distribution of the parts in the egg, 



Italic figures represent dry weight only. 



