Chromosomes in Germ-Cells of Culex 213 



in both somatic and germ cells of various plants, the clearest cases 

 being described by Overton ('09) in Thalictrum purpurascens and 

 Calycanthus floridus. 



In a number of spindles, most of them from one testis, the left 

 hand chromosome pair {a) of Fig. 23 was found irregularly frag- 

 mented (Figs. 37, 38, 39), and even unequally divided as in Figs. 

 40 and 41. These cases of fragmentation were very rare and were 

 found among a larger number of cells containing normal groups 

 of chromosomes, but constrictions such as appear in Fig. 23, a, 

 were frequent. Fig. 42 shows a still deeper constriction in the 

 same chromosome. These cases of fragmentation and constric- 

 tion suggest that this particular chromosome pair may be com- 

 posite, and I should therefore not be surprised to find other species 

 of Culex with a larger number of pairs of smaller chromosomes, 

 or even to find more than the expected number in somatic cells 

 of this species. 



In the telophase of the first maturation division the chromosome 

 fuse and then large vacuoles appear as in Figs. 43 and 44. Later 

 one finds a distinct nuclear membrane and chromosomes lying on 

 this membrane as in Fig. 45, where cell a is drawn to show an 

 optical section through the nucleus, and cell b a tangential section. 

 In the prophase of the second division (Fig. 46) the chromosomes 

 are already divided longitudinally, and they always come into the 

 spindle divided and much tangled (Fig. 47). As in the first divi- 

 sion the spindle forms in the elongated nucleus. In the anaphase 

 the V-shaped chromosomes move out of the tangled metaphase 

 and form regular polar groups (Figs. 48 and 49). A telophase 

 is shown in Fig. 50. 



As a final effort to decide whether the smaller pair of chromo- 

 somes is equal or unequal, I went through my sections again and 

 made camera drawings of the plainest cases of prophase group- 

 ing and of the various metaphase forms (Figs. 51 and 52). The 

 components of the pair in prophase are always more or less 

 twisted and foreshortened, so that a slight difference like that in- 

 dicated in Fig. II might be difficult to detect. In Fig. 51,0 to i/ 

 are from prophasesof the first spermatocyte, e from a late sperma- 

 togonial prophase. Similar cases may be seen in the metaphases 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY VOL. S. NO 2. 



