THE INCUBATION OF HENS' EGGS 



177 



to tlie A'itelline memhrane is a layer of very dense wliite 

 wliich is prolonged toward the large and the small ends of 

 the egg, respectively, in two whitish, convoluted strands 

 called chalazffi (Figure 82). The two chalazse are twisted in 

 opposite directions. The line describing the long axis of 

 the egg will pass through tlie bases of the two chalaziie and 

 be at right angles to the axis of the yolk passing through 

 the center of the blastoderm. 



Surrounchng and continuing this dense white is a spiral 

 layer of somewhat less dense white which is in turn 



Fin. H'2 



blasfoclerm 



cuticle 



shell 



\.^oul('r-sheJ/ rnmiirdne 

 ^rcell 

 i_ chalaza 

 inner shell membrane 

 ^.^dense ivhile 



liquid v.hife 



dark yolk 

 L iK^ht Ljolk 



vitelline membrane 



Farts (if an e^ 



surrounded by a thin, watery white. Tlie difference between 

 the dense and thin white is easily noted when a new-laid 

 egg is broken into a saucer.' The spiral formation of the 

 white may be noted by carefully dissecting a hard-boiled egg. 

 One of the functions of the white is to prevent micro- 

 organisms from reaching the germ spot. To this end it lias 

 marked liactericidal jiroperties. Once in the yolk, liacteria 

 are safe, for the yolk has no defensive pro])erties. The shell 

 memlirane consists of two lax'ers, a thick outer layer next to 



' Src FiguiT 236, \>\\&- 49;i, 



12 



