236 CHARLES W. METZ 



to note that at certain stages in prophase the figures of all three 

 (somatic, first maturation and second maturation) divisions 

 are superficially very similar, although the actual processes in 

 the three cases are very different. 



Fucellia marina (figs. 106-110). As in the previous case, so 

 in the present, the paired relationship of the chromosomes is 

 essentially like that described for the Muscidae and Sarcopha- 

 gidae, and requires no detailed description. A few somatic 

 prophases have been reproduced to show the origin of the chro- 

 mosomes in the former in the forai of closely paired threads, 

 and the subsequent disjunction of these into the less closely 

 associated condensed chromosomes found in metaphase. Figure 

 106 is an early prophase showing the six bivalent threads. Fig- 

 ures 107 and 108 are somewhat later stages illustrating the sepa- 

 ration of the threads. All three are complete (diploid) figures. 

 The most interesting features observed in Fucellia are those 

 shown by prophases containing multiple (probably tetraploid) 

 groups (figs. 109, 110). Each chromatic aggregate in these, 

 contains four (or eight) chromosomes instead of the usual pair, 

 (compare with figs. 96 and 97 and see pp. 252 and 253). 



Ophyra leucostoma (figs. 111-114). In most of the Diptera 

 studied so far great difficulty has been experienced in analysing 

 telophase figures. Usually the chromatin is so massed at this 

 point that no details whatever can be distinguished. In the 

 present species, however, a few figures have been obtained, 

 which although far from satisfactory, are nevertheless sufficient 

 to show something of the chromosomal behavior during this 

 stage. Two of these are shown in figures 111 and 112. They 

 suffice to show the loop or U-shape of the chromosomes, and sug- 

 gest the process of reticulation that is taking place as the chroma- 

 tin becomes diffuse. The polarity of these U-shaped threads 

 bears a significant relation to the similar polarity evident in 

 early prophase when the chromosomes reappear (figs. 100 and 

 101). The chromosome group and the pairing phenomena of 

 Ophyra are practically the same as those of Homalomya and 

 FuceUia. Figure 113 shows a late diploid (spermatogonial) 

 prophase with six pairs of chromosomes, some of which already 



