SOMATIC MITOSES OF THE MOSQUITO 585 



ing the ovogonial and spermatogonial chromsomes Miss Stevens 

 ('10) has reported much the same cytological conditions in Culex 

 pipiens as have been found by Metz and Whiting. "Each of 

 the six chromosomes divides longitudinally, and the pairing of 

 the daughter chromosomes probably occurs in the telophase, for 

 very early prophases show the chromosomes paired and twisted 

 together, forming three spireme threads which gradually shorten 

 and separate for mitosis." 



Miss Taylor reports three chromosomes for a number of somatic 

 cells but fails to find any cells showing six. She figures a split 

 appearing at the ends of some of the chromosomes, which con- 

 dition I find in poorly fixed material. The split indicates the 

 beginning of the line along which two chromosomes have fused. 

 Her failure to find six may be due to imperfect fixation, as may be 

 judged from her figures. The importance of proper fixation has 

 already been emphasized. 



In the case of Culex pipiens it is evident that when a sper- 

 matozoa with three chromosomes unites with an egg with three 

 chromosomes the somatic number of six is produced. The 

 comparatively little work which has been done on somatic 

 mitosis has tended to show that the behavior of the somatic 

 chromosomes may not always be the same as that of those of 

 the germ cells. (Hoy '16.) By this I do not mean that the 

 differences which seem to exist need in any way interfere with 

 the current cytological hypotheses, although other writers seem 

 to think so. It is quite evident that in Culex pipiens there is 

 no difference between the two groups of cells. It will be of 

 interest in this connection to review the chief literature dealing 

 with the body chromosomes. A discussion of the results will not 

 be attempted at present. 



The breaking up of the chromosomes in the somatic cells of 

 Ascaris is too well known to need further discussion. 



In Morril's work ('10) the drawings of the somatic chromo- 

 somes in Archimerus alteratus, Anasa tristis and Chalinidea 

 vittigera are generally larger and longer than those of the repro- 

 ductive cells. The relative proportions of the two sets of chromo- 

 somes appear to be the same, however. In an Anasa tristis 



