CHROMOSOME STUDIES IN THE DIPTERA 47 



it may be assumed that both sexes agree, save as regards the two 

 sex-chromosomes (heterochromosomes) . 



No attempt is made in this paper to elaborate the data. That 

 can be done only after a more extensive study, and one involving 

 more species. Likewise the figures have been limited to a number 

 sufficient merely to illustrate the essential facts. 



TYPE I 



Chromosome groups found in Drosophila amoena, D. ampelophila, 

 D. quinaria, and two species as yet unnamed 



Figures 1 to 5 show metaphase plates of chromosome groups 

 designated as Type I. Figure 1 is a diploid group of D. amoena 

 female. Figures 2 and 3 are corresponding groups from males of 

 the same species, introduced here for reference. In figures 4 and 

 5 similar groups are shown for D. ampelophila females. Figure 

 1 is from a section and indicates the normal relations of the chro- 

 mosomes, except that one member of the small pair is hidden. 

 The other four are from aceto-carmine smear preparations, and 

 consequently show the chromosomes somewhat out of place or 

 disarranged. Yet the essential similarity of all five figures is 

 quite evident, and in each one the same constellation of chromo- 

 somes is readily seen. It is this constellation that is termed 

 Type I. 



If now, we examine any one of the figures, for instance figure 

 5, we immediately distinguish three different sorts of chromo- 

 somes on the basis of differences in size and form. The first sort 

 is very small and spherical (fig. 5, m), the second elongate, rod- 

 like or curved (fig. 5, h), and the third very long, more or less 

 V-shaped and constricted in the middle (fig. 5, I). As a rule 

 these chromosomes are definitely associated in pairs, there being 

 in this group one pair of the first sort, one of the second, and two 

 of the third — four pairs in all. The three classes, separated thus 

 according to size and shape, are also distinguished by character- 

 istic differences in behavior, which exhibit themselves in meta- 

 phase, anaphase and prophase. Upon this basis they may be 

 named and characterized as follows: 



