FURTHER STUDIES ON HETEROCHROMOSOMES IN 



MOSQUITOES. 



N. M. STEVENS. 



In my study on the chromosomes in the germ cells of Culex, 

 published in March, 1910 ('10), there were three figures (n, 20 

 and 21) which differed from all others for Culex, in showing an 

 unequal pair of chromosomes in the spermatogonia (Fig. u), 

 and a condensed pair in the growth stage of the spermatocytes 

 (Figs. 20 and 21). At the time when the proof of that paper was 

 corrected, it was suspected that the three figures referred to 

 belonged to another species, probably Anopheles punctipennis, a 

 few larvae of Anopheles having, it was supposed, been collected 

 in the net with Culex, and having escaped detection in both larva 

 and pupa stage. 



In October of this year (1910) an abundant supply of Anopheles 

 larvae was secured and a satisfactory study of both male and 

 female germ cells made, showing without question that in the 

 male Anopheles punctipennis there is present an unequal pair of 

 heterochromosomes, attached to one of the equal pairs, but other- 

 wise exactly comparable to the unequal pair described by the 

 author for nine species of Muscidae ('08). A careful reexami- 

 nation of the germ cells of Culex pipiens, and a study of Culex 

 tarsalis and Theobaldia incidens in California during the summer, 

 revealed no such heterochromosomes in those species. A de- 

 scription of the chromosomes in the germ cells of Anopheles 

 punctipennis and Theobaldia incidens will be given in the fol- 

 lowing pages. 



Methods. The germ glands of both Anopheles and Theobaldia 

 were studied both in-acetocarmine preparations and in sections 

 of material fixed in Flemming and stained with iron-haematoxylin 

 or thionin. The latter stain gave very satisfactory results with 

 this material, and saved much time in preparing the sections for 

 study. 



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