FERTILITY AND STERILITY IN DROSOPHILA 357 



Hole stock. I shall also consider the behavior of the fertility of 

 the extracted truncates (extracted after crossing out to a wild 

 stock) when tested together and when back-crossed into their low- 

 producing and high-producing grandparents. 



FERTILITY OF THE EXTRACTED TRUNCATES 



I wish to deal first with the evidence that bears on the question 

 raised in Part II, as to whether or not the fertility of the truncate 

 stock can be raised by outcrossing. In other words is low fertility 

 in this case a concomitant of the truncate wing condition, or can 

 high fertility be transferred to the truncate stock by crossing it 

 out to a wild stock and extracting? 



To answer this question a truncate female was crossed to a 

 Woods Hole male. This cross I shall refer to as A. The recipro- 

 cal cross in which the truncate male was mated to the Woods 

 Hole female I shall refer to as B. There were five bottles of the 

 Pi made up in each case. A large number of the Fi were mated in 

 pairs and the truncates selected from their offspring. 



The fertility of the extracted truncates was then tested by means 

 of the following combinations : 



1. A truncate female (F2 extracted from the truncate grand- 

 mother) was mated with four of her truncate brothers. 



2. A truncate female (F2 extracted from the truncate grand- 

 father) was mated with four of her truncate brothers. 



3. Control: The fertility of the original truncates was tested by 

 placing a number of males with a single female in each case. 



The results of this test are recorded in tables 1, 2 and 3. 

 The fertility of the extracted truncates when tested together is 

 almost 50 per cent, while the fertility of the truncates used for 

 control is only 22.6 per cent. In other words, from a source of fer- 

 tility of 63.4 per cent (Woods Hole stock; Part III, table 3b, no. 8) 

 there has been transferred to the truncate winged forms (orig- 

 inally with a fertility of about 20 per cent) about 25 per cent 

 of additional fertility. The increase in fertility is the same in 

 this case whether the truncate male or female is used as the 

 grandparent. 



