The Germ Cells of Diptera 365 



second spermatocyte mitosis, though they frequently show the 

 preparatory split in the anaphase (Fig. 49). We have here an 

 unusually clear demonstration of the essential facts of synapsis 

 and reduction, together with the rather unusual phenomenon of 

 conjugation of homologous chromosomes in cells outside the 

 sphere of maturation. Prophases of the second spermatocyte 

 mitosis in Scatophaga appear in Figs. 50 and 51, and metaphases 

 in Tetanocera in Figs. 52 and 53. An oogonial prophase and 

 anaphase are given in Figs. 54 and 55, and a late prophase for 

 Tetanocera in Fig. 56. 



These two species as well as the one following belong to the 

 Acalyptrate Muscidae. 



8 Drosophila arnpelophila 



Drosophila has been placed at the end of the list of Muscidae 

 because of the pecuHarities which occur in the behavior of its 

 chromosomes and the difficulties which have been encountered in 

 their interpretation. While in Sarcophaga all the stages neces- 

 sary for a description of the behavior of the heterochromosomes 

 of both sexes were found in the course of a few hours' work on 

 perhaps ten or twelve preparations, satisfactory results in the case 

 of Drosophila have been obtained only after a prolonged study 

 extending over more than a year and involving the dissection and 

 examination of some two thousand individuals. Sectioning the 

 material has never given satisfactory results. Hermann's platino- 

 osmic solution and Worcester's formal-sublimate gave the best 

 fixation, but the division stages are so scattering that permanent 

 preparations, even if good fixation were secured, seemed less prac- 

 tical than the aceto-carmine method, which is much quicker and 

 gives clearer pictures of the mitotic phenomena when they are 

 present. 



Spermatogonial mitoses are not abundant, and cells in which 

 perfectly clear equatorial plates can be studied are exceedingly 

 rare. The chromosomes in prophase are paired and twisted 

 together in such a manner that it has. been impossible to make an 

 intelligible drawing of them in an early prophase. In Fig. 57, a 



