PERTILITY AND STERILITY IN DROSOPHILA 

 AMPELOPHILA 



IV. EFFECTS ON FERTILITY OF CROSSING WITHIN AND 

 WITHOUT AN INCONSTANT STOCK OF DROSOPHtLA 



ROSCOE R. HYDE 



Department of Zoology, Coluvihia University 



, ELEVEN DIAGRAMS 



INTRODUCTION 



In Part II of these studies it was shown that although the mu- 

 tant stock truncate, produced a large number of fertile sperm and 

 fertile eggs, yet when the truncate female was mated to the trun- 

 cate male only 20 per cent of the eggs hatched. It was also shown 

 that the truncates were not a homogeneous stock, for the flies 

 with truncate wings give rise to offspring some of which have 

 long wings like those of the wild flies. This has held true through 

 many generations of continuous selection. These long winged 

 flies in turn are also not homogeneous because they throw some 

 truncates, and this has held despite some twenty (estimated) 

 generations of selection. ^ A peculiar phenomenon shown by the 

 long wings is that their fertility when tested together is about twice 

 as great as that shown by their truncate brothers and sisters when 

 tested together. 



I wish here to present in detail the evidence that bears on the 

 result of crossing within this inconstant stock; and the effects on 

 fertility when both forms are crossed into a wild stock — the Woods 



1 Since both forms are under study in this paper it is convenient to refer to this 

 stock as an "inconstant stock." 



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