770 RATE OF GROWTH OF DOMESTIC FOWL 



The mammal was seen to go through at least three cycles during 

 its growth period ; if the tricyclic theory of growth is also true for the 

 bird, then the fowl must go through a complete cycle during its 

 embryonic period of growth. Figs. 3 and 4, curves of the embryonic 

 period of growth, show this to be the fact;^-!*^ indeed it seems as if 

 the curve of the embryonic period of growth shows two cycles with 

 maxima at A and B. 



SUMMARY. 



This paper points out the fact that the growth period of the do- 

 mestic fowl is analogous to that of the mammal, being composed of 

 three, or perhaps four, cycles ; two of these cycles are postembryonic 

 with maxima at about 8 and 18 weeks varying somewhat with the 

 breed and two or at least one, are embryonic with maxima at 11 to 

 12 and 15 to 16 days of age. Hatching occurs during the first part 

 of the second or third cycle resembUng in this respect the guinea 

 pig" rather than the mouse. ^ The velocity curves of each of these 

 cycles are similar to and can be represented by the equation of an 

 autocatalytic monomolecular reaction. 



The author is indebted to Mr. H. L. Kempster, Department of 

 Poultry Husbandry of this Station for supplying him with some 

 references in this paper. 



^ Lamson, G. H., and Edmond, H. D., Stons Agric Exp. Station, Bull. 76, 1914. 



1" Hasselbalch, K. A., Skand. Arch. Physiol, 1900, x, 364. 



" Read, J. M., Arch. Entwcklngsmechn. Organ., 1912-13, xxxv, 708. 



