Fig. i i . — Tail-length against total length 



during growth in the mouse, Phenacomys 



longicaudus ; logarithmic plotting. 



k = about i -41. 



(Recalculated from the data of Taylor, 1915, p. 129.) 



100 130 160 ZOO 



total length, mm. 



15 



20 



30 40 50 60 70 8090100 



dorsal facet number 



150 ZOO 



300 



Fig. 12. — Relation of facet-number in dorsal and ventral lobes of mutant 

 female fruit-flies of the bar-eye series ; logarithmic plotting. With decreasing 

 temperature, the total number of facets in the eye increases ; but the number 

 in the ventral lobe of the eye increases heterogonically relative to the number 



in the dorsal lobe. 



The curve on the right denotes heterozygotes between bar and wild-type (full eye). In the curve 

 on the left, x denotes homozygous ultra-bar and heterozygotes between ultra-bar and bar ; o, 

 heterozygotes between ultra-bar and wild-type ;• , homozygous bar. 



k for all is close to 1-5 ; 6 is lowered by admixture of the wild-type gene, and is at its maximum 

 in pure ultra-bar (i.e. rises with decreasing absolute size of the eye). It is clear that facet-formation 

 must begin ontogenetically in the dorsal lobe. 



22 



