CASTLE. — INBREEDING, CROSS-BREEDING, AND SELECTION. 779 



the correlation is greater in A 61 than in A 6, it is not materially greater 

 in the former than in the not-inbred X series. The close resemblance 

 between A 61 and X 1 is probably due to the fact that they were reared 

 under similar conditions. 



In Table XXVIII are brought together for comparison constants 

 derived from the several correlation tables, XXI-XXVII. From a 



Individuals 

 35 



3D 



To 



■20 



13 



10 



Length «^ 

 of Tibia 28 29 30 31 32 33 3" 1 35 3 6 37 38 39 40 41 42 43 « 45 



Figure 7. Variation in length of tibia of one hundred males from each of four 

 different series ; A, from generation A 61 ; M, from M 31 ; N, from N 30; and 

 X, from X 1. 



study of this we learn the close dependence of the variability of Droso- 

 phila upon external conditions. Compared with these factors inbreeding 

 is of little consequence. 



The well-nourished cultures (A 61, 3131, and X 1, Figures 6 and 7) 

 show a higher mean number of spines and a greater tibial length than 

 cultures reared under poor or variable conditions of nutrition, such as 



