The Germ Cells of Dipiera 369 



mosomes in a loosely branched condition. Fig. 90 s an early 

 prophase in which the heterochromosome pair is very compact and 

 deeply stained, while the other chromosomes are granular and 

 denser in some parts than in others. A later prophase (Fig. 91), 

 from a section, shows the heterochromosome pair assuming the 

 cross-shape which we find in the later metaphase. Fig. 92 is a 

 polar view of the equatorial plate of the first spermatocyte; and 

 Figs, 93 and 94, side views of the spindle to show the cross-shaped 

 heterochromosome bivalent in two positions. Here the crosg 

 (Fig. 94), instead of having opposite arms equal, as in cross- 

 shaped tetrads composed of equal elements, has one of the ver- 

 tical arms longer. It is evident from Figs. 93 and 95 that the 

 longer arm is the smaller heterochromosome, while the remainder 

 of the cross is the larger member of the pair. The larger ele- 

 ment is folded in the same manner as in Drosophila (Figs. 66 and 

 67) but the smaller element is attached by one end instead of by the 

 middle as in Drosophila. The second spermatocyte mitosis pro- 

 ceeds as in the other forms and presents nothing of especial interest. 

 Dimorphism of the spermatozoa is foreshadowed by the first sper- 

 matocyte anaphases (Figs. 96 and 97). In the female the clearest 

 figures were obtained from ovarian follicle cells (Figs. 98 and 99). 

 The pairs are equal and comparison with the spermatogonia! 

 chromosome group (Fig. 86) indicates that the equal heterochro- 

 mosome pair is one of the two longest. 



The general results for the nine species of flies are the same; i. e., 

 an unequal pair of heterochromosomes in the male leading to 

 dimorphism of the spermatozoa, and a corresponding equal pair 

 in the female, each equivalent to the larger heterochromosome of 

 the male: also a prereductional pairing of homologous chromo- 

 somes in the prophase of mitosis in spermatogonia, oogonia, and 

 ovarian follicle cells. 



DISCUSSION 



I Sex Determination 



So far as I know there is no published work on the heterochro- 

 mosomes of the Diptera. The literature on the heterochromo- 



