244 CHARLES W. METZ 



ogous autosomes. Figure 162 shows the X and Y -chromosomes 

 separating froni one another in the reduction division. Figures 

 163, 164 are second spermatocyte groups showing the X-con- 

 taining and Y-containing classes. 



Stratiomyidae 



Ptecticus trivittatus. No differences in chromosome behavior 

 (so far as the paired association is concerned) have been found 

 to distinguish this species from those previously considered. 

 P. trivittatus possesses eight pairs of chromosomes, of which 

 the smallest is the unequal sex-chromosome pair. 



Culicidae 



Culex pipiens (figs. 165-171). Since exception has been 

 taken to the observations of Stevens on the chromosomes of 

 Culex pipiens (see p. 221), I have made a careful study of this 

 species in order to determine whether any fundamental differ- 

 ences exist between it and the higher Diptera with regard to 

 chromosome pairing, but I am not able to find such differences. 

 My studies are based upon spermatogonia and ovarian cells 

 from larvae and pupae. In these I find the six chromosomes 

 closely associated in pairs during prophase (fig. 165), dissociat- 

 ing somewhat in late prophase, and arranging themselves " side 

 by side in a flat plate during metaphase (figs. 166-168) just as 

 in the other Diptera. There is no evidence whatever, in my 

 material, of a separation (reduction) of the two members 

 of a pair during anaphase such as described by Taylor and by 

 Lomen. On the contrary, anaphase figures clearly show each 

 chromosome dividing and sending daughter halves to the poles. 

 Figure 170 (a portion of an early spermatogonial anaphase in 

 side view) shows the manner in which each individual chromo- 

 some divides. Figure 169 shows a later stage of a typical 

 anaphase (spermatogonial) also in side view, in which six chromo- ' 

 somes (three pairs) are each undergoing a division. At this 

 stage the chromosomes are in the form of double V's each of 

 which is a daughter chromosome attached at its apex to a spindle 



