470 Journal of Agriculture. Victoria. \ 11 Aug., 1919. 



In nature, it is generally notifod, by the observant breeder, that thi- 

 sex of offspring usually favours the parent who is in the greatest danger 

 of extermination. Those hens which go bare and red about the head 

 and face, and which are very hard in feather, only moulting odd feathers 

 at a time, and laying almost throughout the year, will generally give in 

 rhe autumn a fairly high ])ereentage of females. On the other hand, 

 the hens which have gone through a complete moult, and have come into 

 full vigour, will show a majority of cockerc^ls in the earlier hatches. The 

 problem of sex control is of such vast importance that it merits the 

 most thorough investigations, as in the light breeds the cost and labour 

 of rearing cockerels are barely balanced by the market returns. 



Development of the Embryo. 



During the first day there are two growth centres, the head process 

 and the primitive streak, the latter appearing in the blastoderm in the 

 axial line of the future embryo, but somewhat behind the place where 

 the embryo proper begins to develop. In the head process there is the 

 first development of the spinal nerve, as well as a rod of cells termed 

 the notochord, which form the supporting and stiffening axis of the body, 

 and there is a thin membrane termed the amnion (or caul), which forms 

 a closed sac surrounding the embryo. 



The second day the head continues to develop rapidly, and the for- 

 mation of blood vessels begins, the heart being formed within the head 

 fold, with vitelline veins and vitelline arteries. Two swellings from the 

 brain form the first trace of the optic system, and the ears are represented 

 by two slight depressions where the hind brain will ultimately develop. 



The third day marks the commencement of the internal organs, with 

 a considerable reduction of the white of the egg, caused by the increased 

 activity of the blood-vessel system. 



The fourth day the white, or albumen, of the egg is further reduc;'d, 

 the wings and legs appear as conical buds, the kidney is also developed, 

 and the amnion is fully formed and completely surrounds the embryo. 

 By the fifth day the legs and wings have increased in length, although 

 they are still very much alike. 



The sixth day the avian characteristics have develo])tHl in the legs 

 and wings, head and alimentary canal. Hitherto there has been little 

 distinction from the embryo of mammals or reptiles. 



The seventh day the head ceases to grow more rapidly than the 

 body, and motion becomes apparent. Feathers begin to appear on the 

 ninth day, but do not protrude until the thirteenth day. 



The beak appears on the eighth day, and by the sixteenth day the 

 beak and nails have hardened. By the fourteenth day the chicken 

 changes its position from lying at right angles to the axis of the egg, 

 and thereafter lies lengthways. By the twentieth day the chicken pierces 

 the inner shell membrane, and commences to breathe air, consequently 

 the allantois circulation gives way to that of the lungs. The twenty-first 

 day the chicken hatches, prior to which the remainder of the yolk is 

 absorbed, providing sufficient nourishment for about 24 hours or so. 



