286 



ANIMAL PHYSIOLOGY. 



kikes no part in the process. In succeeding parts of tlio 

 oviduct, the albumen and the shell are deposited. If a hen's 

 egg be placed on its side, and the shell be broken on the side 

 which happens to be uppermost, the cicatricula is always 

 found on the corresponding part of the yelk. The reason of 

 this is, that the albumen first deposited round the vitelline 

 membrane is prolonged in two twisted strings, chalazce, 



Fig. 150. CLEAVAGE OF CICATRICULA OF HEN'S EG a. After Coste. 



towards the extremities of the egg, to be there retained, to a 



certain extent, in position. By these chalaz83 the yolk is 



suspended, and being 

 lighter on the side on 

 which the cicatricula is 

 placed, it turns that 

 part always upwards 

 away from the damp 

 ground, and towards the 

 warmth of the hen's 

 body. In consequence 

 of this arrangement, 

 there is nothing easier 



'Fig. 151. HEN'S EGG, showing chalazoe, than to 'obtain a view 

 and embryo of three days incuba- f ^ earl gt of 



tion, with area vasculosa around it. , Jo, 



embryonic growth in 



the chick, from the appearance of the primitive groove 

 onwards. If it be sought to hatch the eggs artificially, care 

 must he taken not to allow their temperature to vary more 

 than a few degrees above or below 102F. 



&09. The primitive groove is the future cerebro-spinal canal, 



