CASTLE. — INBREEDING, CROSS-BREEDING, AND SELECTION. 777 



of food in the thirtieth generation, and the measurements were made 

 from dry dead flies found in the bottom of the jar. This culture shows 

 a unique variability. Series A, M, and X were breeding under the 

 same good conditions and side by side when the specimens were taken 

 for special study. 



Out of the preserved material of each of the four series one hundred 



TABLE XXII. 



Correlation in Number of Spines between Sex-combs of Right and 

 Left Legs, Series A, Generation 61. 



Left leg (x). 



A x = 10.58 

 A y = 10.50 



ax = 1.087 

 <r;j = 1.136 



r = 0.469 ± -05261 



males were selected at random, the measurements being made as follows : 

 The fly was held on its back, under a dissecting microscope, by needle 

 points, and the right and left fore legs of the fly were then pulled off and 

 laid on a glass slide. Next, the right hind leg was pulled off, and also laid 

 on the slide. These parts were then covered with a cover glass, and 

 examined under a compound microscope. The number of spines in each 

 sex-comb was counted and recorded. The length of the tibia of the 

 hind leg was ascertained by means of an ocular micrometer, the record 



