ASSOCIATION OF CHROMOSOMES IN DIPTERA 239 



Syrphidae 



Eristalis tenax. My studies in this species have included 

 pupae as well as adults, and in both I have found the chromo- 

 some behavior to agree with that in the cases described above, 

 and with Stevens' ('08) description. 



Eristalis hastardi (fig. 123); Volucella obesa (figs. 124-126); 

 Mesogramma marginata (figs. 127, 128). These three species 

 are very different from one another in appearance, but their 

 chromosomes appear very similar (save for minor details of 

 size relations) and hence will be considered together. Figure 

 123 (Eristalis bastardi) represents part of a prophase figure 

 showing the bivalent chromatic threads which are comparable 

 in every way with those seen in Homalomya, Sarcophage, etc. 

 Figures 124 and 125 are metaphases (spermatogonial) of Volu- 

 cella, and clearly show the paired relationship. In the former 

 one chromosome is missing, leaving a single member (in left 

 margin of group) without a mate, but otherwise all are paired. 

 This species is particularly interesting because of the differ- 

 ent sizes apparent in its chromosomes. One pair is easily recog- 

 nized by its large, and one (sex-chromosome) by its small size, 

 and even the others show slight differences from one another. 

 Figure 126 is a first spermatocyte division for comparison with 

 the diploid groups; note the unequal X and Y chromosomes, 

 which are paired in the diploid groups. Figures 127 and 128 

 (spermatogonial) of M. marginata are of significance only in 

 showing the paired arrangement of the chromosomes. 



Sepsidae 



Piophila casei. There is no marked distinction between P. 

 casei and the various species of Muscidae and Sarcophagidae, 

 either in chromosome numbers and size relations or in the general 

 chromosome behavior. 



Bombyliidae 



Anthrax lateralis (figs. 129-133). No more conspicuous cases 

 of chromosome pairing have come to my attention than those 



