WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. 103 



Of recent work on the Diptera, I may mention that of Stevens and 

 of Taylor on Culex, and that of Metz on Drosophila. Stevens ('10a) 

 finds parasynapsis in Culex, not merely in the growth-period of 

 spermatogenesis, but among other kinds of cells. She says ('10a, 

 p. 208) : — " That parasynapsis occurs immediately after the last 

 oogonial mitosis is certain and it is equally certain that the chromo- 

 somes are similarly paired in earlier generations of the oogonia," 

 Again (p. 209) : — " In Culex it is quite certain that parasynapsis 

 occurs in each cell generation of the germ cells in the telophase," and 

 (p. 212), "It is interesting to find in Culex a clear case of parasynap- 

 sis in oogonia, oocytes, spermatogonia, and spermatocyte prophases 

 and then to see the same chromosome pairs appearing in the first 

 maturation metakinesis as though united end-to-end." (It is prob- 

 able that she has overlooked stages in the postspireme showing the 

 changes undergone by a parasynaptic spireme segment in its trans- 

 formation into a metaphase tetrad). Miss Stevens found six to be 

 the somatic number of chromosomes in Culex, the reduced number 

 being three. The side-by-side pairing of the chromosomes in nearly 

 all generations of cells studied, gave the appearance of a reduced 

 number in many situations where it would not have been suspected. 

 Taylor ('14) states that she found in Culex pipiens only three chromo- 

 somes in all the stages that she studied, i. e. in both the somatic and 

 germ-cells of both sexes. This is a very surprising result, but an 

 explanation may perhaps be found in the conditions observed by Miss 

 Stevens, namely, the tendency for the chromosomes in all kinds of 

 cells to pair between mitoses. A poor fixation might easily prevent 

 one from recognizing the double nature of a closely adhering pair 

 of chromosomes. Besides, Miss Taylor found some cells with six 

 chromosomes, and shows figures of some others with more than three. 

 It would seem more reasonable, then, to regard the prevalence of the 

 reduced number found by Miss Taylor as the result of the constantly 

 recurring tendency of the chromosomes to unite side-by-side between 

 successive mitoses, and possibly to poor fixation. 



The results of Metz (*14) on Drosophila are interesting in this 

 connection, for he reports conditions in these flies similar to those 

 found in the mosquito. In this he confirms the earlier results of 

 Stevens ('08). He finds (p. 55) that: — "The chromosomes not only 

 exhibit a close association in pairs at nearly all times, but that before 

 every cell division the members of each pair become so intimately 

 united that they may be said actually to conjugate. Each pair, with 

 the possible exception of the sex chromosomes, goes through what 



