CHROMOSOME STUDIES IN THE DIPTERA 51 



significant fact is that each of the small autosomes resembles in size, 

 for??! and behavior one arm, or one end of a large autosome. So that 

 by assuming a partition of the large autosomes at their median, 

 constricted points, and assuming that each of the resulting halves 

 behaved after separation just as it did before, exactly such a con- 

 dition would be brought about as that found in Type II. 



TYPE III 

 Chromosome groups found in Drosophila funebris 



The important features in this type are shown in figures 14 to 

 17, and diagram 3 a and 3 b. In the main it agrees essentially 

 with Type II except that the m-chromosome pair appears to be 

 entirely lacking (compare figs. 8 and 14). Whether this disap- 

 pearance has been brought about by the degeneration of the pair 

 or by a fusion with some other pair I have been unable to deter- 

 mine. The unusual length of the sex-chromosomes might suggest 

 the latter, but in view of the radical difference in behavior between 

 them and the autosomes, and the fact that another type (V) also 

 lacks the ?w-chromosomes, without a corresponding enlargement 

 of the sex-chromosomes, I am inclined to doubt this explanation. 



It is worthy of note that in this type (III) the sex-chromosomes 

 are fully as elongate as the large autosomes of Type I, yet they 

 retain their own characteristic form and behavior, and show no 

 evidence of the V- or dumb-bell-shape, or a median attachment to 

 the spindle fibers. If it were true that all chromosomes are quali- 

 tatively alike, and that form and behavior are merely secondary 

 characteristics determined by size and bulk, then we should expect 

 these long sex-chromosomes to assume the characteristics of the 

 large autosomes of Type I, but as a matter of fact they do nothing 

 of the sort. To my mind there is no clearer demonstration than 

 this of a qualitative difference between the individual chromo- 

 somes of a group. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGT, VOL. 17, NO. 1 



