OF MUTANT CHARACTERS. 177 



In culture B 9 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 B 9.1, 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 propor- 

 tion as expected. In the F 2 (table 28) 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 27) and 36 per cent (table 29) 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 "invia- 

 bility;" but a consideration of the "in viability" met with in the case 

 of rudimentary (Morgan, 1912) had just led to two new conceptions: 

 first, that the power of fertilization possessed by a gamete is influenced 

 by its somatic environment prior to maturation; second, that a given 

 type of egg 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 account 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 rudimentary. The 

 principle of "repugnance" was exemplified by the cross of rudimentary 

 by rudimentary, which gave no offspring whatever, though repeated 

 fully 100 times, and although both the male and female give offspring 

 when out-crossed. The rudimentary females are usually sterile, and 

 never give more than a few offspring (nearly all females) when out- 

 crossed to unrelated males. 



The shortage of vestigials in the above crosses was thought to be 

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

 of vestigial the effects of prematuration and repugnance were not as 

 great in degree. On the basis of these results, an analysis of the extent 

 to which each of these principles contribute to the "inviability" of 

 vestigial was undertaken by Mr. G. L. Carver (results not yet pub- 

 lished). In Mr. Carver's investigation it was assumed that the short- 

 age in these experiments had been largely due to a cause intrinsic in 

 the vestigial itself, for which reason any stock of vestigial should be 

 equally valid for the test. The stocks used in the above experiments 



