276 CALVIN B. BRIDGES 



In culture B9 a jaunty (jaunty 4) appeared which gave rise 

 to a stock similar to the original jaunty, but so far as known of 

 separate origin. 



In three or four of the cultures, for example, in B9.1, arc wings 

 (arc 6) appeared, and these were indistinguishable from the 

 original arc, though quite certainly of different origin. 



Since these early experiments many other mutations have 

 arisen in experiments involving purple, but these need no 

 special mention here. 



THE INVIABILITY OF VESTIGIAL— PREMATURATION, 

 REPUGNANCE, LETHALS 



One of the most striking features of these crosses involving 

 purple and vestigial was the failure of vestigial to appear in as 

 high a proportion as expected. In the F2 (table 2) where 25 per 

 cent of the flies were expected to be vestigial, only 12 per 

 cent were vestigial; in the back crosses where half of the flies 

 were expected to be vestigial, only 29 per cent (table 1) and 36 

 per cent (table 3) were vestigial. That is, only about half as 

 many vestigials as were expected appeared in these back crosses. 



Such a condition is usually described by the blanket term 

 'in viability;' but a consideration of the ' in viability' met with in 

 the case of rudimentary (Morgan, '12) had just led to two new 

 conceptions: first, that the power of fertilization possessed by a 

 given gamete is influenced by its genetic environment prior to 

 maturation; second, that a given type of gamete is less likely to 

 produce a viable zygote with one than with another of two classes 

 of sperm. The conception of 'prematuration' was used to ac- 

 count for the fact that a rudimentary-bearing egg from a pure 

 rudimentary female is much less able to give a viable offspring 

 than a like egg from a mother only heterozygous for rudi- 

 mentary. The principle of 'repugnance' was exemplified by 

 the cross of rudimentary by rudimentary, which gave no offspring 

 whatever though repeated several hundred times and although 

 both the male and female give offspring when outcrossed. 



The shortage of vestigials in the above crosses was thought to 

 be parallel to the results given by rudimentary, except that in the 



