CHROMOSOMES OF MOSQUITO 541 



C. MITOSES OF THE THORACIC HYPODERMIS 



The developing limb buds and wing buds of the thoracic 

 hypodermis of the larvae show numerous mitotic figures. Three 

 pairs of chromosomes appear in late prophase (figs. 112 and 113), 

 one pair, b, smaller than the other two, a and c. Metaphases 

 stage A, (figs. 114 and 115) and stage B (figs. 116 and 117) are 

 similar to the corresponding stages of spermatogonial and ova- 

 rian mitoses. Figure 118 is a side view of a chromosome splitting 

 in early anaphase and figure 119 shows the six chromosomes 

 lying parallel to each other as they go towards the poles. The 

 chromosomes in figure 119 are V-shaped but only one arm of 

 each V can be shown. The relatively greater tendency of the 

 chromosomes to appear fused in the drawings from hypodermal 

 cells is due to the fact that fixation is interfered with by the 

 chitinous part of the integument. This will be discussed more 

 fully under Technique. More detailed description of the somatic 

 complexes will appear in papers by Mr. Hance and Miss Holt. 



D. SUMMARY OF OBSERVATIONS 



The chromosomes of Culex pipiens are six in number in all 

 diploid mitoses. At all stages the homologues tend to be approxi- 

 mated in three pairs. One pair is smaller than the other two. 



As the chromosomes of diploid cells are passing from prophase 

 to- anaphase, they occupy a flat metaphase plate. Two succes- 

 sive stages, A and B, are distinguished in the metaphase. In 

 stage A the chromosomes are bent rods, swollen at the ends and 

 constricted in the middle. The middles tend to be nearer than 

 the ends to the centre of the plate. 



In stage B the chromosomes tend to be of more uniform 

 diameter. The pairs assume an arrangement parallel to each 

 other, which is continued into the anaphase. Division of each 

 chromosome begins at the middle and the daughters pass to the 

 poles as Vs. 



In the late prophase of the first spermatocyte the approxi- 

 mated pairs become crosses or rings. The chromatids of each 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 2 



