234 



T. H. MORGAN-. 



Pure stock of the double recessive spot black being on hand, 

 a male was crossed to a yellow female. The FI were yellow flies, 

 65 males and 20 females without spot, showing again the domi- 

 nance of yellow to spot in the "compound" y-y a . These FI flies 

 inbred gave: 



Yellow $. Yellow Black 9. Yellow cf- Yellow Black cf- Spot Black cf- Spot cf- 



126 37 33 26 ii 26 



A male of the spot black stock was also bred to a black female. 

 The offspring were black males and females, which inbred in four 

 lots gave the following results: 



In these mass cultures, although an attempt was made to have 

 the food conditions favorable, yet, owing to crowding, the spot 

 black males ran far behind the black males. 



There appeared in the above Fo a yellow black fly with no 

 trace of spot. Since in some cultures (but not here) the spot 

 may be faint and difficult to detect with certainty, it seemed 

 possible that the fly was such a somatic variant. He was tested 

 by breeding to a black female. The offspring were black (very 

 few in number). These inbred gave: 



Had the male in question been only a somatic condition of 

 yellow (suppressed spot) we should have expected some spot 

 males in the % generation. Since none at all appeared there can 

 be no doubt that the grandparent was in reality a yellow black 

 individual both somatically and gametically. The most prob- 



