52 THE UNIVERSITY OF OKLAHOMA 



XXIV. A PRELIMINARY NOTE ON THE CHROMOSOME 



NUMBER OF THE FIRST SPERMATOCYTE OF 



BRUCHUS 



Frank G. Brooks 



f'Vom the Zoological Laboratory of the University of Oklahoma. 



CoutriLution No. 21, Second Series. From the Department of 



Biology of Oklahoma City College. 



Bruchus quadrimaculatiis Fal)r., commonly known as the four- 

 spotted cowpea weevil has come to the notice of the geneticists as 

 being an insect which readily adapts itself to breeding experiments. 

 Since considerable work has already been done, chiefly by Breiten- 

 becker, on the inheritance of Bruchus and since more work is likely 

 to follow, a knowledge of its chromosome number and of the general 

 facts concerning its sperm.atogenesis is desirable. 



The difficulties attendant upon the study of coleopteran sper- 

 matogenesis are well known. Due to the smallness of the cells, the 

 difficulty of fixation and the necessity of dissecting out the genital 

 organs, good slides are procured only by painstaking and irksome 

 proceedure. After the slides are prepared there are irregularities 

 m the spermatogenesis which further complicate the problem. 



The literature along the line of this study is meager. Although 

 some phase of gam.etogenesis has been studied in about seventy 

 species of beetles, complete work has been done in only three or 

 four cases. Most investigators considered their tasks completed 

 after they had demonstrated an unequal pair of heterochromosomes. 

 Miss Stevens has worked on about forty-five species but since she 

 is concerned chiefly with the sex chromosome, her work is limited to 

 this phase of the study. Ethel Browne Harvey, Shelford and Bor- 

 das have done extensive work upon different phases of the problem. 

 Goldsmith's work on tiger beetles, however, constitutes what is 

 probably the most comprehensive investigation that has been made. 



Since, theref-ore, the literature on the subject is meager and the 

 irregularities many, a study of the spermatogenesis of Bruchus has 

 cytological as well as genetic value. 



In this paper the observations are limited to the first spermato- 

 cyte stage. Of course the thing of outstanding importance is the 

 chromosome number. The writer is able to demonstrate clearly 

 that the haploid number of chromosomes for the species is ten. A 

 very common occurrence in my material is a cell showing a polar 

 view of the equatorial plate. In such a cell, eight chromosomes 

 may be seen to form an imperfect oval in which are located two 

 other chromosomes as seen in figure 1 of Plate IV. One chromo- 

 some is always seen out of focus. This is the X-chromosome which 



