254 c - w - METZ - 



In its general features spermatogenesis in Dasyllis resembles 

 that in Asihts scriccits, as described by Metz and Nonidez ('21), 

 and no attempt will be made to give a complete account here. The 

 technique employed in the present work was the same as that 

 described in the preceding paper. The material was fixed in 

 strong Flamming and stained in Heidenhain's iron haematoxylin. 



Dasyllis is unique among the Diptera thus far studied in pos- 

 sessing an unpaired X-chromosome in the male. This is true of 

 all the material I have studied in the genus. The other Diptera 

 have all been of the X-Y type. In an earlier paper (Metz, '16, 

 p. 243) Dasyllis was tentatively considered to possess a Y-chromo- 

 some, but additional material has shown clearly that no Y is 

 present unless it is so minute as to be practically invisible. 



I am indebted to Miss M. S. Moses for assistance in the labo- 

 rious work of examining the ovaries in connection with the obser- 

 vations on oogenesis, and to Miss Ruth Lincks for making the 

 drawings for the accompanying figures. 



SPERM ATOGONIA. 



The spermatogonial chromosome group of D. grossa consists of 

 three pairs of V-shaped and one pair of J-shaped (atelomitic) 

 autosomes, and the unpaired X, as shown in Fig. I. The J-shaped 

 pair appears straight in this figure, but in later metaphases its sub- 

 terminal spindle fiber attachment is evident. The V-shaped pairs 

 are of different sizes, the smallest being readily distinguishable 

 from the other two. Thus the X and two of the autosome pairs 

 may be identified individually. 



As in all of the other Diptera that I have studied, the paired 

 association of chromosomes is persistent through successive 

 spermatogonial generations, and into the final spermatogonial 

 anaphase. In spermatogonial prophases (Figs. 2 and 3) the pair- 

 ing of the large chromosomes does not seem to be as intimate 

 medially as in most other flies a fact which suggests that the 

 peculiar repulsion or lack of attraction exhibited in the growth 

 period is existent here also. 



THE SPERMATOCYTE GROWTH PERIOD. 



In Dasyllis the spermatocyte nucleus is relatively large at the 

 beginning of the growth period; and partly on this account, per- 



