3OO E. C. FAUST. 



ir and il. It will be noticed, however, that 2r has 30.78^ as a 

 mode of higher frequency, w r hile 2! has 27.54/4 as a mode of 

 higher frequency. 



Preparations jr and jl. Of 3r only three hundred individuals 

 were measured, because this comprised the total number that 

 was present in the testis. Of 3! five hundred individuals were 

 measured. The curve of 3r is shown in Fig. 8. It is bimodal in 

 character, but with a greater number of individuals grouped 

 around the lower mode. The plot for 3! is shown in Fig. 9. It 

 is unmistakably unimodal in appearance, with the mode at 

 30.78^, the length where the upper mode of the preceding bimodal 

 curves occurred. Comparison with the bimodal curves shows 

 plainly that it is the upper half of a bimodal curve, such as that 

 shown in Fig. 2. 



Preparations 4r and 4!. In these preparations four hundred 

 spermatozoa from each testis were measured. 4r is shown in 

 Fig. n, and 4! in Fig. 12. These are both bimodal and show 

 the dimorphic nature of the spermatozoa, although they differ 

 considerably from the bilaterally symmetrical type. 



Preparations made at Woods Hole in August, 1913, from adult 

 males were measured to check the foregoing data. When plotted 

 as a variability curve, they, too, yielded a bimodal curve, \vith 

 modes at the same lengths as those in the preparations Ir and il. 



IV. DISCUSSION. 



The data presented in the previous section show very distinctly 

 the dimorphic character of the spermatozoa of Anasa tristis. 

 On the basis of the chromatic-rod length they fall into two classes, 

 those with an extra amount of chromatin, and those without 

 such an additional amount. Whatever differences and vari- 

 ations there are among the several curves, the differentiation 

 into two groups remains proved. Such minor deviations as 

 occur are probably due to secondary factors not yet discovered, 

 and do not directly affect the bimodal grouping. 



This pronounced dimorphic character of the spermatozoa of 

 Anasa tristis must bear some fundamental relation to the di- 

 morphism of chromosome number demonstrated by spermato- 

 genesis studies. It is altogether probable that the mature 



