22 



MASS. EXPERIMENT STATION BULLETIN 344 



in porosity. The proportions actually obtained were 3.7 normal to 1 medium 

 or high in porosity. It is probable that the so-called high-porosity or thin- 

 shelled eggs come from females pure for the factor po after the shell glands 

 have been somewhat exhausted by continuous laying. 



D. Egg Shape 



A number of different indexes have been developed for egg shape to compen- 

 sate for the varying diameter of the egg in relation to length. For general 

 purposes the index proposed by Pearl and Curtis (1916) is adequate. Here the 

 ratio of maximum diameter to maximum length is given. A normal index 

 according to these workers is .7452. Eggs measured in the Massachusetts 

 Station flock of Rhode Island Reds gave an index of .7338 which is in close 

 agreement with the index of .731 reported by Axelsson (1936). 



Egg shape, according to extensive studies by Asmundson (1931), is governed 

 largely by the muscular activity of the oviduct. Since individual hens lay 

 eggs of a characteristic shape, it is probable that the coordination of the various 

 physiological processes varies between individuals. 



In the studies to be reported on egg shape the classification was made not 

 on the basis of measurements but purely on observation. Three general classes 

 of eggs were described — long, round, and normal. Eggs with too great a 

 length in proportion to diameter fell into the first class. Those eggs that were 

 too blunt and lacked length were placed in the second class. All other eggs 

 were considered normal in shape. 



Table 9. — Egg Shape 



Data are very limited on the use of dams for breeding that laid either long or 

 round eggs. The limited number of long-egg dams produced a high percentage 

 of normal daughters. The great majority of the dams used for breeding laid 

 normal-shaped eggs. These dams averaged to produce about 90 percent of 

 normal daughters. The large-egg line C gave a slightly greater percentage of 

 long-egg daughters than occurred in the other two lines. The combined data 

 in table 9 do not indicate that egg shape is governed by inherited factors. 



