PRINCIPAL AXIS OF SYMMETRY IN THE BIRD'S EGG. 



345 



TABLE III. (Pigeon No. 5.) 



further evidence that extremes of variation in the axis angles 

 are due to the failure of an ovum to orient itself in the oviduct 

 with reference to its long axis. The nine extreme variants of 

 this bird showed irregularities in the development of the chalazae 

 or other abnormalities. The long axis was well marked in all 

 but three eggs. Clutch 611 is typical; 



First egg (7 somites )2i.3 mm. (long axis) 19.5 mm. (transverse axis), 19.0 mm. 



(polar axis). 

 Second egg (4 somites) 21.0 mm. (long axis) 19.8 mm. (transverse axis), 18.0 mm. 



(polar axis). 



Although only three of this bird's eggs had abnormal embryos 

 and all twelve eggs that were incubated hatched, yet her eggs 

 showed the greatest variability (Fig. 3, 5) , a fact which, as has been 

 said, is to be correlated with the abnormal oviduct. One extreme 

 observed was 5, this was a very abnormal egg as the chalazae 

 were not attached to the yolk at all but to the outside of the dense 

 albumen. The greatest variation was 84 among the normal eggs. 



Pigeon No. 6. This bird was hatched January 30, 1911, but 

 did not mate until eight months later. The first egg was laid 

 October 29, 1911. Since there were 7 infertile eggs in the next 

 13 clutches, the male was killed and five months later she mated 

 again with the bird indicated on page 343. In the following 

 two years and two months 24 clutches were laid. The observa- 

 tions had to be discontinued before she ceased to lay, but as she 

 was four years old at the time and had begun to lay numerous 

 abnormal and infertile eggs this record represents practically all 

 her reproductive activity. The high percentage of infertile eggs 

 during the first year was undoubtedly due to her first mate; 

 nevertheless her layings were very irregular and could never be 

 predicted. The curve (Fig. 3, 6} shows that the axis angles varied 



