Linkage Group VI. 51 



VII. LINKAGE GROUP VI. 



After much of the present paper had been written, a new mutant 

 character appeared which bears considerable resemblance to the 

 fourth-chromosome character "bent" in D. melanogaster. On 

 account of this resemblance it is also called bent. It has not been 

 studied fully, but, as indicated below, it does not appear to be in 

 any of the preceding linkage groups. 



Bent (be). (Plate 5, Figure 2.) 



Description. — Bent appears to involve modifications in three separate parts of the 

 fly — legs, wings, and eyes. None of these is absolutely constant, however. The 

 legs vary from normal to a condition in which they are very much shortened and 

 more or less distorted. The first part affected seems to be the basal tarsal joint on 

 the hind legs, which is often greatly shortened and may be thickened, when the legs 

 are otherwise nearly normal. Different degrees of modification of the hind legs are 

 shown in figure 2 of plate 5. The leg on the left in this figure is from a fly from 

 normal stock, those on the right are from bent stock. The effect on the wings is 

 less marked and is seldom observed. Usually only one wing is affected. The modi- 

 fication resembles the short wing types in concave (plate 3, fig. 6), and frequently 

 involves a partial spreading of the wings. The sharp bend near the base of the wing 

 characteristic of bent in melanogaster is lacking, or at least is much less marked. 



The eye modification may be described as speckled. Small dark specks appear 

 here and there over the eye surface, due apparently to irregularities in the small 

 hairs between the ommatidia. The speckling of the eye is practically constant, 

 although very slight in some individuals. 



It is possible that the speckling of the eye is a distinct mutant character, due to a 

 different gene from that responsible for the other two modifications, but this seems 

 highly improbable. It arose with bent and appears to be inseparable from bent. 



Bent is greatly influenced by environmental conditions. Some bottles of pure 

 stock give mostly normal flies, with the "bent" ones appearing mainlj'^ toward the 

 end of the hatch. Preliminary experiments indicate that crowding, dryness, or poor 

 food conditions favor the development of the leg and wing modifications. When 

 mass cultures and pair matings were carried on side by side, the mass cultures gave 

 a higher percentage of flies exhibiting the leg modification. The flies from the pair 

 matings were considerably larger and better fed than those in the mass cultures. 



Origin. — (M 346.) From a pair mating made to test for a possible short bristle 

 character, the Pi female was removed and put in a fresh bottle with an Fi male. 

 The small-bristle character failed to materialize, but in the latter culture several 

 flies were found which had short tarsi on the hind legs. These were especially marked 

 among the last flies that hatched. Altogether 15 females and 10 males vdih. short 

 hind legs were obtained, together with 57 females and 40 males that were not 

 noticeably affected. The separation was made on the basis of the legs alone, as 

 the eye modification was not noticed until afterwards. The Pi female and the 

 male used in the second bottle had normal legs. 



Comparison. — Bent appears to correspond closely to the bent of melanogaster in 

 its effect on the legs. The wing modification is somewhat similar to, but is not so 

 nearly a duplicate of, that in melanogaster. In both species the character is very 

 variable and dependent on environment. The same stock may give at one time 

 almost all normal appearing flies and at another time almost all bent flies. We 

 have reared one culture of bent melanogaster in a small v\bX under crowded conditions 

 and found that practically all exhibited the leg modification, which suggests that 

 crowding may have the same effect here as in virilis. In these respects, then, the 



