82 
Scientific Proceedings (42). 
bacilli in the feces is relatively large or small would appear to 
depend upon the stage of the disease in the individual animals. It 
is important to point out, that even in well-nourished and appar- 
ently healthy herds of reacting animals (such as those used in this 
work) there are likely to be, at all times, a few animals actually 
passing virulent tubercle bacilli in the feces. 
A detailed account of this work is published in Bulletin No. 
149 of the Illinois Agricultural Experimental Station. 
49 (574) 
An alteration of the sex-ratio induced by hybridisation. 
By T. H. MORGAN 
[From the Department of Zoology, Columbia University.] 
Males and females of the fly Drosophila amphelophila occur 
in nature in about equal numbers. A long series of experiments 
failed to induce any change in the sex-ratio by adding different 
sugars, salts, acids or alkalies to the food on which the larvae live. 
A remarkable alteration of the sex-ratio took place, however, in 
the second generation of certain crosses between two races that 
arose as mutations. When a male of a race with rudimentary 
(" short truncated") wings was crossed to a female of a race with 
short proportionate wings all of the females had normal wings and 
all of the males short proportionate wings, like the mother. When 
these (Fi) were inbred, there were produced in the second genera- 
tion three classes of individuals according to the character of 
the wings; namely, long (normal), short proportionate, and short 
rudimentary distributed according to sex as shown below: 
Long 9 Long cf Propt 9 Propt <? Rudim 9 Rudim d 1 
989 137 336 389 8 I 2 
The normal males are to the females as one to seven, while in 
the other two classes the sex ratio is approximately normal. The 
point of prime importance is that it is the normal males that are 
affected. Even if we assumed that the deficiency might be due to 
the absence (in part) of males with rudimentary wings, and double 
the number of males with normal wings, the number of normal 
males would still fall far below that of the females. 
