AUTHOR'S ABSTRACT OF THIS PAPER ISSUED BY 

 THE BIBLIOGRAPHIC SERVICE, MARCH l6, IC>2I. 



THE CHROMOSOMES OF PSEUDOCOCCUS NIP^E. 



FRANZ SCHRADER, 

 BRYN MAWR COLLEGE. 



INTRODUCTION. 



In the course of some work on sex determination in the dif- 

 ferent species of Pseudococcus a genus of the Homoptera 

 very peculiar conditions were met with in the chromosome be- 

 havior. These peculiarities were observed especially in Pseudo- 

 coccus nipcc (identified by H. Morrison, Bureau of Entomology), 

 and it is of this species that the present account is given. A more 

 detailed report, covering other species of Pseudococcus as well, 

 is reserved for a later paper. 



Most of the material was fixed in Allen's modification of 

 Benin's fluid. On the whole, fixation is more or less difficult ; 

 and at best the cells are somewhat small. The main features are 

 clear cut, however, and hardly to be mistaken. I am indebted to 

 Professor E. B. Wilson and to Professor C. E. McClung who 

 examined some of my slides and offered helpful criticism. 



THE CHROMOSOMES IN THE FEMALE. 



The number of somatic chromosomes in the female is ten, with 

 little or no size and form differentiation. Counts are made with 

 little difficulty in various cells, but oogonial cells furnish of 

 course the best criterion. Generally the chromosomes are counted 

 most easily just before they .have become arranged in a meta- 

 phase plate. There can be no doubt as to their number (Fig. 6). 

 A detailed study of the maturation phenomena in the female was 

 not made. Suffice it to say that five tetrads are formed and that 

 these are normal in appearance ; they are very much like those 

 formed in the oogenesis of many other Homoptera (Fig. /). 

 The reduction process is thus probably not unusual. 



SPERM ATOGENESIS. 



The somatic number of chromosomes in the male is also ten, 

 and as in the female these seem to be alike in size and shape. 



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