238 CHARLES W. METZ 



dae (figs. 4-20) having a similar chromosome group. In Chae- 

 topsis no good figures of early spermatogonia! prophases have 

 been secured, owing to the small size of the nuclei, and to dif- 

 ficulties in fixation. Metaphases, however, are distinct (figs. 

 117-118) and plainly show the paired arrangement of the chromo- 

 somes. These, when compared with maturation divisions show- 

 ing the haploid group (fig. 119, first division) leave no doubt 

 of the relations in this species. 



Camptoneura picta (figs. 120, 121). Since C. picta shows 

 pairing relations similar to those in the last named species it 

 attracts attention only because it differs so markedly from 

 Chaetopsis in respect to the number and size relations of its 

 chromosomes. As a matter of fact Chaetopsis excites the greater 

 interest, for Camptoneura has the chromosome group (fig. 

 120, diploid, and 121, haploid) found in several families (all 

 those above mentioned, as well as the Sapromyzidae, Micrope- 

 zidae, Sepsidae, Syrphidae, and one species of Bombyliidae), 

 while the group found in Chaetopsis is found in no other species 

 I have studied outside the Drosophilidae. 



Sapromyzidae 



Physegenua vittata (fig. 122). I have had difficulty in ob- 

 taining suitable material from Sapromyzid flies, but as in the 

 case of the Trypetidae enough has been secured to determine 

 the essential point — that the chromosomes are associated in pairs. 

 Figure 122 (spermatogonium) represents one of the few com- 

 plete polar views found. It is seen somewhat diagonally, with 

 the result that some of the pairs appear to lie beneath the others, 

 but in reality they form an almost flat plate, entirely comparable 

 with those seen in the Muscidae, etc. The two small chromo- 

 somes are doubtless the sex-chromosomes (X Y), just as are 

 the small ones in the Muscidae. 



Drosophilidae 



(See pp. 222-224, "Reality of chromosome pairing." For spe- 

 cific references see explanation of plates; also. Metz '14.) 



