54 Additional Characters. 



VIII. ADDITIONAL CHARACTERS. 



In addition to the above characters whose linkage relations are 

 known to some extent, the following characters have been found, 

 but have not yet been placed with certainty in any linkage group. 

 These are characters that are difficult to test for linkage, because of 

 poor viability, irregularity of appearance, or interference with the 

 classification of other characters. Since the linkage tests have not 

 been completed, none of the data are included here. 



Extra (E). (Plate 5, Figure 3.) 



Description. — Extra is a dominant character somewhat like the sex-linked domi- 

 nant triangle. It is not uniform in appearance, but usually takes the form of a V- 

 shaped branch above the second vein near its apex. Occasionally it is lacking and 

 the fly appears normal. In combination "svith the other wing characters, concave, 

 confluent, pinched, or branched, extreme effects are produced. In the first case the 

 wing is apt to be crinkled and the costal vein thick around the end of the wing. In 

 the others more extra veins appear than would come from the sum of the two char- 

 acters acting alone. With confluent the effect of both characters is exaggerated; an 

 irregular network of veins is apt to be present, and thickenings appear at the junction 

 of cross-veins and longitudinal veins. With pinched, extra veins appear not only 

 above the second vein, but also between the third and fourth (the region affected by 

 pinched). With branched a cluster of veins usually appears in both the region 

 normally affected by extra and in that normally affected by branched. When all 

 three characters — pinched, branched and extra — are combined, the three correspond- 

 ing clusters of veins appear (plate 4, fig. 3). 



Origin. — (M 21.) Among the offspring of a spine female by confluent (dominant) 

 concave males one confluent female appeared with net-like wings. When mated to 

 normal-appearing brothers this female produced the following classes of offspring: 

 confluent 16, extreme confluent (net-like) 39, wild-type 39, and extra vein 19. This 

 and subsequent matings indicate that the net-lilce condition in the confluent flies and 

 the extra-vein condition in part of the others is due to the same gene — that for 

 "e.xtra." 



Spine (sn). (Plate 5, Figure 4.) 



Description. — The only distinguishing characteristic that we have been able to 

 detect in spine is the presence of a small bristle arising from one of the sense-organs 

 on the third vein opposite the posterior cross-vein. It is very inconstant in appear- 

 ance, frequently being absent or present in only one wing. It ordinarily behaves as 

 a recessive, but in at least one case it was manifest in an Fi fly from an out-cross, 

 which suggests that it may occasionally act as a dominant. 



Origin. — (E 1286.) One male from pinched stock, found by Mr. M. Demerec. 



Capsule (op). 



Description. — Capsule is a recessive character affecting the wings. As the name 

 implies, the wing is swollen and cylindrical like a capsule. AU trace of venation is 

 gone. Both wings are bladder-like and stand out at right angles from the thorax. 

 The viability and fertility of capsule flies are very poor and the stock was lost before 

 linkage tests were made. The males appeared to be sterile, although only a few 

 were tested. In the heterozygous condition capsule has an exaggerating effect on 

 confluent, as shown in figure 2 of plate 3. All of the confluent flies from a cross of 

 confluent by a capsule were of this extreme tj^pe. 



