The Germ Cells of Diptera 363 



(Fig. 20). The metaphase of the first spermatocyte division is 

 shown in Figs. 21 and 22, and prophases of the two kinds of second 

 spermatocytes in Figs. 23 and 24. The spermatozoa would evi- 

 dently be dimorphic as in the other species. 



^ Sarcophaga sarracinice 



The three species of Diptera whose spermatogenesis has already 

 been described belong to the sub-family Muscinae, while Sarcoph- 

 aga is a member of the sub-family Sarcophaginae, The number 

 of chromosomes in Sarcophaga is the same as in the other species, 

 12 somatic and 6 reduced, and the heterochromosomes closely 

 resemble those in CaUiphora. The spermatogonial plate (Fig. 

 25) shows the 12 chromosomes paired, but separated ready for 

 metakinesis, and one chromosome shows the division fine. In 

 the growth stage (Fig. 26) the pair of heterochromosomes comes 

 out clearly in the midst of diffuse and irregular masses of faintly 

 stained chromatin. In these flies the ordinary chromosomes 

 become much branched or diffusely granular in the growth stage 

 but do not unite to form a spireme of even width as in so many 

 forms. Whether or not they unite end-to-end at any stage before 

 or after synapsis I cannot say. A prophase and an equatorial 

 plate of the first spermatocyte mitosis may be seen in Figs. 27 and 

 28, and the metaphase and anaphase in Figs. 29, 30 and 31. The 

 polar views of the metaphase of the second mitosis (Figs. 32 and 

 33) of course show dimorphism as to the heterochromosomes 

 (Ai, /zj). Equal division of all of the chromosomes follows as in 

 the three preceding species. Figs. 34 and 35 were drawn from 

 adjacent oogonia in metaphase to show the close longitudinal 

 pairing of the chromosomes and their later separation before 

 metakinesis. The equal heterochromosomes are usually found 

 together in the middle of the plate and each one is evidently equiv- 

 alent in size to the larger heterochromosome of the spermato- 

 gonia and spermatocytes (Figs. 25 to i^). Fig. 36 is from an 

 ovarian folhcle cell. The four figures, 25, 34, 35 and 36 show the 

 pairing of homologous chromosomes in spermatogonia, oogonia 

 and somatic cells. 



