VARIATION IN HEAD LENGTH OF SPERMATOZOA 509 



group containing the female-determining spermatozoa exceeds 

 the other in numbers. On the basis of the cytological evidence 

 we should expect the two groups to be equal but there is a great 

 deal of evidence in both cytological and experimental data to 

 indicate that one kind is often more numerous than the other. 



E. B. Wilson ('06) has described two kinds of spermatids for 

 this species, one containing six and the other seven chromosomes. 

 In the absence of figures it is not possible to determine an ex- 

 pected ratio. Since this species also is a Coreid, the ratio of 

 1.00 : 1.11 determined from the chromosomes of Anasa is of 

 interest. It agrees fairly closely with the measurements of head- 

 lengths in this as well as in the last species. 



3. Reduviolusferus, Si \iemiptera,n. The material was collected 

 during March and gave active spermatozoa. The results of the 

 live hundred measurements are given in figure 4. The fre- 



Fig. 3 Leptocoris trivittatus; frequencj- distribution of head-lengths of 984 

 spermatozoa from a single testis. 



Value in 20.9 21.3 21.6 22.0 22.3 22.7 23.0 23.3 23.7 



Frequency 1 2 3 6 9 13 18 23 25 



24.0 24.4 24.7 25.0 25.4 25.7 26.1 26.4 26.7 

 26 28 30 41 53 37 31 38 40 



27.1 27.4 27.8 28.1 28.4 28.8 29.1 29.5 29.8 

 41 50 60 51 45 41 39 38 40 



30.1 30.5 30.9 31.2 31.6 31.9 32.3 32.6 33.0 

 31 24 20 15 12 11 8 7 5 



Fig. 4 Reduviolus ferus; frequency distribution of head-lengths of 500 sper- 

 matozoa from a single testis. 



Value in 23.7 24.0 24,4 24.7 25.0 25.4 25.7 26.1 26.4 



Frequency 4 5 6 5 12 19 25 30 35 



26.7 27.1 27.4 27.8 28.1 28.4 28.8 29.1 29.5 

 36 49 56 45 33 27 35 22 18 



29.8 30.1 30.5 '30.9 31.2 31.6 31.9 32.3 32.6 

 18 10 9 8 7 5 4 2 1 



Fig. 5 Euschistus variolarius; frequency distribution of head-lengths of 500 

 spermatozoa from a single testis. 



Value in microns 13.0 13.4 13.7 14.1 14.4 14.7 15.1 15.5 15.8 



Frequency 6 16 20 21 24 46 60 39 38 



16.1 16.5 16.8 17.2 17.5 17.9 18.2 18.5 

 58 84 38 12 7 6 6 3 



