INHERITANCE OF EGG CHARACTERS 21 



C. Shell Porosity 



Porosity has been reported to vary according to the number of shell pores 

 and the number of pores in the external and internal shell membranes (Hays, 

 1927). In the present studies porosity was roughly determined by a physical 

 examination of the general surface texture of the shell. Eggs were thus grouped 

 as high, medium or low in porosity. The data are summarized in Table 8 for 

 the three lines through eight generations. 



Table 8. — Egg-Shell Porosity 



Daughters Classified by Egg-Sbc-li Porosity 

 Dams Classified by Egg-Shell Number of- 



Porosity Dams High Medium Low Percent 



Low 



High porosity 

 Line A 

 Line B 

 Line C 



Medium porosity 

 Line A 

 Line B 

 Line C 



Low porosity 

 Line A 

 Line B 

 Line C 



Few data are available on the high-porosity group of dams. Eggs in this 

 class are for the most part soft shelled and generally do not pass successfully 

 through the incubation period. Even though a considerable number of birds 

 laying these highly porous eggs were placed in the mating pens during this 

 experiment they failed to produce a sufficient number of chicks to warrant the 

 retention of their daughters for a year of trapnest records. 



The group of dams laying eggs of medium porosity showed a rather uniform 

 proportion of low-porosity daughters in the three lines. About half the 

 daughters showed low porosity, the other half being classed as of medium or 

 high porosity. The small-egg line A gave a somewhat greater proportion of 

 high-porosity daughters than the other two lines. 



The low-porosity group may be considered as normal with respect to shell 

 porosity. A comparison of the three lines here shows that line B gave more 

 normal daughters and that lines A and C produced about three-fourths normal 

 to one-fourth medium or high in porosity. Genetically, high or medium po- 

 rosity seems to depend on one recessive gene po. If the medium porosity dams 

 are of the formula po po and are mated with males of the formula Po po, half 

 the daughters will show normal porosity. Table 8 shows a close approximation 

 to this proportion. These data are in general agreement with those of Axelsson 

 cited by Landauer (1937). 



Normal dams gave about three normal daughters to one with medium or 

 high porosity. If these dams were of the genetic formula Po po and were mated 

 to males of the formula Po po, three-fourths of the daughters would be normal 



