Chromosomes m Germ-Cells of Culex 21 1 



continuous. In Fig. 15 one double end was seen above the plas- 

 mosome, and a segment with both ends free at a lower focus. 

 From this stage on, the three chromatin threads shorten, thicken, 

 and each separates into its two parallel components. Fig. 16 

 is an early prophase showing the three long twisted pairs. Fig. 17 

 a later stage with shorter, thicker twists, and Fig. 18 a slightly 

 later stage from a section, showing a very characteristic appear- 

 ance of the three pairs about the time that the spindle is formed. 

 Fig. 19 is also from a section, and shows the plasmosome still 

 present but pale again. In both testes from one individual, 

 examined in aceto-carmine preparations, there was one cyst of 

 prophase stages, two of which are shown in Figs. 20 and 21, where 

 one pair of chromosomes was condensed while the others were 

 still pale and granular. The material was collected on November 

 22, after freezing weather, and a very unusual number of cells 

 were in the prophase and metaphase of the first maturation mito- 

 sis. The chromosomes and cells were both smaller than usual, 

 and I thought that maturation must have been hastened by high 

 temperature following cold, and that the stages shown in Figs. 

 20 and 21 were abnormal. Later, however, I found a trace of 

 the same phenomenon in perfectly normal material well fixed with 

 Flemming and stained with thionin; i. e., one pair of chromosomes 

 becoming condensed in advance of the other two. The con- 

 densed pair in Fig. 21 resembles closely the shorter pair in Fig. 18 

 and other similar stages; and, together with the inequality ob- 

 served in seven spermatogonial equatorial plates (Fig. 11), indi- 

 cates that the smaller pair of chromosomes in Culex may have 

 some of the characteristics of the heterochromosomes of other 

 insects. 



Fig. 22 is a typical first spermatocyte in metaphase or meta- 

 kinesis, the spindle being formed within the elongated nucleus. 

 In Fig. 23 the same chromosomes are shown separately. The 

 middle one {b) is the shorter pair of the spermatogonia and pro- 

 phase stages and the ring is the figure 8 of Fig. 18, h. In rare 

 cases all three pairs may come into the spindle in the form of 

 rings, but usually only one pair takes this form. Fig. 24 is a 

 very frequent prophase appearance, showing one ring with over- 



