3O2 E. C. FAUST. 



In the cases of most evident bilateral symmetry (in numbers 

 ir and il, 2r and 2!), the preparations were made up early in 

 November, when the spermatozoa were still in abundance. In 

 the cases where the curves do not show this bilateral symmetry 

 (in numbers 3r and 3!, 4r and 4!), such a maximum number of 

 mature individuals was not found. In one testis, at least, in 

 each of these pairs (3r and 4r) the majority of the spermatozoa 

 had been ejected from the testis. This fact was shown by the 

 emptiness of the testis upon first examination. We may there- 

 fore provisionally consider the normal condition as one in which 

 there is a maximum number of mature spermatozoa, and the 

 bilaterally symmetrical curve of variability as the best expression of 

 such a norm. 



It might be assumed that this dimorphism in length is due not 

 to any internal factor which marks out two groups of mature 

 spermatozoa, but represents merely a sudden growth in length 

 whereby the maturing spermatozoa pass over the low inter- 

 modal point very rapidly, so that few are "caught" in that place. 

 There are definite reasons why such a theory cannot be accepted. 

 The spermatozoa in the upper and lower reaches of the curve 

 show by their structure that they are equally mature. This is 

 shown not only by their general size and shape, but by their 

 staining reaction which is very different from that of immature 

 spermatozoa. Again, immature forms when they do occur are 

 just as likely to occupy the low intermodal portion of the curve as 

 the mature ones. In fact immature forms have been recorded 

 for such a critical length. Such an objection must be put aside 

 as unjustifiable. 



V. SUMMARY. 



I. The work presented in this paper has proved the presence 

 of size dimorphism in the adult spermatozoa of Anasa tristis. 

 Measurements of the length of the chromatic rod of several 

 hundred spermatozoa from each testis, plotted as a frequency 

 curve, have demonstrated two modes, one between 27. 54^ and 

 28.08/1, and the other between 30.24/1 and 30.78/4, and the data 

 offer adequate support for the conclusion that length dimorphism 

 exists. 



