148 THE SECOND-CHROMOSOME GROUP 



"BROWN" BODY-COLOR. 



Soon after the discovery of black, there appeared in the black stock 

 a few males whose color is a rich "brown" instead of being a clear, 

 cold, greenish black. These flies were in reality a double recessive, as 

 was shown by the F 2 results from the out-crossing of these males to 

 wild females. The other recessive turned out to be "yellow," which 

 is sex-linked. An astounding number of flies (hundreds of thousands) 

 were raised (by Morgan, Wallace, Bridges, and Eleth Cattell) in work- 

 ing out the simple relation of brown to black, to yellow, and to the 

 wild form. A similar interest was shown in the relations of vermilion 

 and pink (the double recessive being called "orange"), these relations 

 being then regarded as highly important from the standpoint of the 

 presence-and-absence theory and the seriation of characters. 



VALUATION. 



Black is a mutation of first rank in value, and has been used more 

 extensively than any other autosomal character. Its viability is 

 excellent. With a little practice black can be separated from the 

 heterozygous form with perfect accuracy. There are no other body- 

 color mutations in the second-chromosome that interfere with the 

 classification of black, and in turn black can be used in experiments 

 with any of them (including speck and streak) without masking effects 

 or confusion. Black has been extensively used in .class work in 

 genetics by beginners; in this case the only caution necessary is in the 

 classification of very young flies, since the full black color is slow to 

 develop. Even experienced workers occasionally put back into the 

 culture-bottle the^very young flies (in a cornucopia, if etherized), 

 and then classify them when they are again taken out at the next 

 counting. 



BALLOON 



(Plate 7, figure 1.) 



The mutant character balloon was found by Morgan (November 

 1910) in a stock culture of truncate flies (Morgan, 1911). This char- 

 acter was first noticed from the fact that certain flies not long emerged 

 from the pupa-case had their wings pumped full of liquid, the two 

 laminae of the wing being separated, except at the edges, to form a 

 balloon (plate 7, fig. 1). As these flies became older these vesicles 

 usually broke or the liquid was resorbed, so that the laminae came 

 together, giving an uneven or blistered appearance to the wing. These 

 wings were held out at a wide angle from the body (plate 7, fig. 1) and 

 this character forms the most quickly recognizable mark of identifi- 

 cation in the separations. The divergence of the wings serves well for 

 a quick and rough preliminary separation, though a more reliable 



