CASTLE. — INBREEDING, CROSS-BREEDING, AND SELECTION. 747 



Experiments of S. 0. Mast. 



The experiments of Mr. Mast, made at various times between Novem- 

 ber, 1903, and May, 1904, support this conclusion in part. Mr. Mast 

 made crosses (5, 5a, 6, and 6a) between flies from generations 31-40 of 

 the A series (which was then producing about 50 young to a pair), and 

 mates taken from two new series, If and A 7 ", which commonly produced 

 200-400 offspring to a pair, or even more (see Figure 2, p. 742, and 

 Tables VIII and IX, pp. 758, 759). 



Av. for fertile pairs, 45 young. 



Av. for pairs 1-6, 274 young 



Mr. Mast also mated females of A 36 (average young to a pair, 45) 

 with males taken from a stock-jar started a short time previously with 

 normal individuals similar to the M and N series. This will be called 

 Cross 7. The reciprocal cross was not made. 



Average, 62 young. 



