304 CHARLES ZELENY 



CONSTANCY OF ULTRA-BAR 



The single mutant male appeared on October 20, 1917, and 

 the new stock was isolated in pure condition on December 27th. 

 Numerous counts at 27° show no essential change in character 

 except for the mutants mentioned in a later paragraph. The 

 mean, range, and standard deviation remain essentially un- 

 changed. The data are given in tables 5 and 6. During the 

 period of establishment of the stock it was subjected to selection, 

 but without any noticeable effect. There is no indication that 

 this selection had any part in the production of the constancy. 

 The selection data are treated in a separate paper. Later counts 

 made during July, 1919, and not given in the tables show that 

 the stock had remained without essential change for twenty 

 months. The differences in the various cultures as shown in 

 tables 5 and 6 are in some cases well within the probable error 

 of random sampling, but in several cases the departures can not 

 be explained in this way. For instance, take such a difference 

 as that between the means of cultures no. 178 and no. 184 which 

 is equal to 1.86 units. Its probable error, Ed = ±\E? + Eo = 

 ± 0.17, is only one-eleventh of the difference. Correspond- 

 ingly, the difference in the, males of the two cultures is 1.71 units 

 and the probable error is 0.16. These differences are therefore 

 in all probability not due to random sampling. Their lack of 

 permanence indicates that they are environmental and not 

 germinal. 



On four occasions individuals have appeared in the ultra-bar 

 stock which differ markedly from the ordinary ones. Three of 

 these may be considered as probably reverse mutations to full 

 and the fourth as a new mutation upward in the direction of bar. 



Mutant A. On July 9, 1918, there appeared in bottle no. 

 496.4 of the ultra-bar stock at 27°C. a female with 46 facets in 

 the left eye and 50 in the right eye. The upper limit of ultra- 

 bar stock females is 35 facets (table 5). It appeared that this 

 female might be a heterozygote with one ultra-bar and one full- 

 eye factor as the facet range of 54 such heterozygotes in test no. 

 357, table 7, is 28 to 49. Accordingly, she was mated with four 



