52 Linkage Group VL 



two mutant races seem to agree. The eye modification, however, is absent or incon- 

 spicuous in melanogaster bent. 



Linkage Tests with Bent. 



The origin of bent indicated that it was an autosomal recessive, and this is borne 

 out by subsequent tests. Since bent was not alwa^'s recognized at first, it is impossible 

 to tell just how man}'^ flies in the original culture were bent. Two matings of normal 

 flies from this bottle both gave bent. Lilcewise matings of bent flies gave bent, 

 apparently pure stocks. Several out-crosses were also made from this bottle and no 

 bent flies were found in Fi in any of these. In F2, however, bent appeared in every 

 bottle. All of these results indicate that bent is a recessive. 



Bent flies from the original culture were out-crossed to confluent garnet pinched 

 flies, to branched flies, and to concave telescoped acute flies. The first four are 

 dominants representing groups II, III, IV, and V respectively, and the last three are 

 recessives from groups II, III, and IV respectively. From the former crosses heter- 

 ozygous males were back-crossed to bent females, and from the others pairs were 

 mated to secure F2 counts. Unfortunately, when this was done it was not known 

 that bent appeared best in crowded bottles, hence most of the offspring appeared 

 normal when the leg modification was used for classifj'ing. However, several cultures 

 of each type were made up and a sufficient number of unquestionable bent flies have 

 appeared to give conclusive results. These experiments are being repeated and the 

 counts need not be given here in detail, but they may be summarized by saying that 

 recombinations were obtained with all of the above characters. Since these included 

 two representatives of groups II, III, and IV, and one from group V, the results seem 

 to show conclusively that bent is in an independent linkage group (group VI) unless 

 some unusual genetic behavior is involved, of which there is no evidence. 



Reasons have already been given for considering linkage groups I to V as repre- 

 senting the five large chromosomes. Bent, therefore, appears to represent the small 

 m-chromosome. 



This fact, together with the resemblance of bent to the bent of melanogaster, which 

 is a fourth, or w-chromosome character, provides evidence for considering the two 

 characters homologous, and for considering the m-chromosomes of the two species 

 homologous. In the case of the large chromosomes such resemblances as those shown 

 by the two bents might well be due to accidental mimicry, but in the minute m-chro- 

 mosomes the chance of such mimicry is reduced to a minimum. 



Net (Nt). (Plate 5, Figure 1.) 



Description. — Net is characterized primarily by its small, slender bristles and by 

 the frequent absence of many of the head bristles. Associated with these are a whole 

 series of minor modifications affecting nearly all parts of the fly. The name is de- 

 rived from the network of veins in extreme specimens. Extra veins or bits of veins 

 appear frequently between the costa and second vein, resembling those of triangle 

 and extra; others appear occasionallj'' between the second and third veins near the 

 apex, and more often in the neighborhood of the posterior cross-veins. The latter 

 resemble those of the character branched. In some specimens no extra veins are 

 present and the wings appear to be normal, while in others the wing is a network of 

 veins. Between the two extremes practically all intermediates appear. Among the 

 other characteristics of net may be mentioned its somewhat smaller size and paler 

 color, the occasional speckling of the eyes like that found in bent, but less extreme, 

 the absence or disarrangement of some of the hairs on the thorax and head, the paler 

 bands on the abdomen and the frequent appearance of abnormalities of the abdominal 

 segments. In some cases the head is denuded of hairs and bristles over the entire 

 interocular region. Rarely a specimen appears in which the eyes and legs are like 



