METHODS OF COLLECTING AND PRESERVING DROSOPHILIN^. 45 



D. simulans, D. funebris, D. ohscura, D. affinis, and D. cardini this 

 difference is quite well marked. 



Size: In most species the males average a little smaller than the 

 females. In the case of D. melanogaster this size difference is a true 

 secondary sexual character, as has been shown by an examination of a 

 large series of gynandromorphs (Morgan and Bridges, 1919). In these 

 specimens male and female parts are combined in the same individual; 

 and it is regularly observed that the male parts are a trifle smaller and 

 bear somewhat smaller bristles and hairs. I have observed the same 

 relation in gynandromorphs of D. simulans. 



Abdominal structure: As has been pointed out above, the abdominal 

 structure of the two sexes is different in the genus Drosophila. The 

 female has seven well-developed dorso-lateral plates, the male only 

 five. The spiracles are correspondingly different — the female has 

 one on the fifth segment and one on the sixth, while the male has two 

 on the fifth. The ventral abdominal plates are also different. The 

 female has six, the male four, and the posterior members of the series 

 are quite different in shape in the two cases. 



IX. METHODS OF COLLECTING AND PRESERVING 



DROSOPHILINAE. 



Most of the Drosophilinse feed on fruit or on fungi, or have leaf- 

 mining larvae. The most efficient places to collect them are where food 

 is plentiful. Fruit in grocery stores will yield the commoner species, 

 and more especially the widely distributed ones that are presumably 

 introduced. Windfall apples or other decaying fruit usually repays 

 examination. Tomato patches, even before the fruit is ripe, are 

 worth sweeping. Garbage piles usually have many species. Fleshy 

 fungi, either agarics or Boletinse, will yield many forms; they are 

 more prolific after they have decayed somewhat. Bleeding trees should 

 always be examined. 



My own practice has been to expose fruit in the woods, and collect 

 from it daily for a while. The fruit is usually placed in a bottle and 

 hung in a low tree. This method makes it less likely to be stolen by 

 small mammals, and makes collecting easy, as one simply pours the 

 flies into his collecting bottle. After a week or so the bottle may be 

 brought in, and the larvae and pupae allowed to develop, thus increasing 

 the collection. For this kind of collecting it is advisable to use many 

 different sorts of fruit. I have found banana, pineapple, tomato, and 

 peach to be specially satisfactory. 



I always bring the collections into the laboratory alive, in order to 

 be able to breed any forms that seem desirable. If this is to be done 

 it is necessary to be careful, especially in the case of sweepings, not 

 to leave predacious forms (spiders, empidids, asilids, ants, etc.) or large 



