512 CHARLES ZELENY AND C. T. SENAY 



a unimodal distribution. It should not, however, be forgotten 

 that the two elements of a population will, when combined, give 

 a unimodal curve in case the modes of the elements are close 

 together. 



Among the coleopterans one, Berosus striatus, has two well 

 marked and equal size groups. The other, Passalus cornutus, 

 has a single size group or two with modes very close together. 



Taking all cases so far described there are twenty-three spe- 

 cies involved, including the one given by Wodsedalek ('13). 

 This is a sufficient sample to justify us in stating that there can 

 be no doubt of the validity of the hypothesis presented. The 

 chromosomal dimorphism of spermatogenesis is represented in 

 the active functional spermatozoa by size dimorphism. Control 

 of sex then merely awaits our ability to separate the two sizes 

 in the living condition and to use them in artificial insemination. 



Fig. 6 Cosmopepla carnifex; frequency distribution of head-lengths of 500 

 spermatozoa from a single testis. 



Value in microns 16.5 16.8 17.2 17.5 17.9 18.2 18.5 18.9 19.2 



Frequency 6 14 16 19 26 42 83 53 35 



19.6 19.9 20,3 20.6 20.9 21.3 21.6 22.0 

 42 68 37 14 11 11 9 8 



Fig. 7 Passalus cornutus; frequency distribution of head-lengths of 500 sper- 

 matozoa from a single testis. 



Value in microns 10.15 10.30 10.45 10.60 10.80 11.00 11.15 



Frequency 1 5 4 9 14 26 27 



11.30 11.50 11.70 11.85 12.00 12.20 12.40 

 46 65 89 65 55 22 29 



12.55 12.70 12.85 13.00 13.20 

 14 12 7 7 2 



Fig. 8 Berosus striatus; frequency distribution of head-lengths of 500 sper- 

 matozoa from a single testis. 



Value in microns 13.7 14.1 14.4 14.7 15.1 15.5 15.8 



Frequency 4 9 9 10 14 32 41 



16.1 16.5 16.8 17.2 17.5 17.9 18.2 

 56 42 30 54 40 36 30 



18.5 18.9 19.2 19.6 19.9 20.3 20.6 

 23 17 16 14 10 4 2 



