208 A^. M. Stevens 



for several weeks, if the material has not been too deeply stained 

 in the beginning. The fixed material was stained either with iron- 

 haematoxylin or with thionin, both giving good results especially 

 with the Flemming fixation. Figures of cells and chromosomes 

 drawn from sections are only about two-thirds as large as those 

 taken from aceto-carmine preparations. The difference is mainly 

 due to shrinkage in fixing fluids and alcohols, though the acetic 

 acid probably swells the structures slightly. The majority of the 

 figures were taken from aceto-carmine preparations and those 

 taken from sections will be designated as such. 



A few oogonia were found in mitosis in various young ovaries. 

 In all cases the chromosomes»were paired in prophases and meta- 

 phases before metakinesis (Figs, i and 2), as previously described 

 by the author in several species of Muscidae ('08). Two longer 

 pairs are present with one pair considerably shorter. The homol- 

 ogous chromosomes composing the pairs are apparently equal in 

 length. As in the Muscidae, each of the six chromosomes divides 

 longitudinally, and pairing of the daughter chromosomes prob- 

 ably occurs m the telophase, for very early prophases show the 

 chromosomes paired and twisted together forming three spireme 

 threads which gradually shorten and separate for mitosis. Fig. 

 3 shows the chromosomes of an oocyte in an early growth stage 

 with the paired chromosomes still distinct, and Fig. 4 the nucleus 

 of a somewhat later stage showing three separate spireme threads 

 of different lengths. Whether these separate spiremes later unite 

 to form a single thread I have been unable to determine, but that 

 parasynapsis occurs immediately after the last oogonial mitosis 

 is certain, and it is equally certain that the chromosomes are sim- 

 ilarly paired in earlier generations of the oogonia. 



Fig. 5 is an outhne camera drawing of a testis stained m aceto- 

 carmine and considerably flattened under the cover-glass. In 

 the first cyst at the tip {a) were resting spermatogonia, in the sec- 

 ond {b) anaphases and telophases of spermatogonial mitoses. 

 Then followed cysts {c,d,e) containing synizesis stages, and growth 

 stages of the first spermatocytes, one cyst (/) in a stage immedi- 

 ately following the first maturation division, several cysts of sperma- 

 tids {g, h, t, j) and masses of spermatozoa (k) pressed out through 



