DIMORPHISM IN SPERMATOZOA OF ANASA. 



295 



brought it out clearly. Because the posterior limit of the 

 chromatic rod is more easily located than the anterior limit, all 

 measurements were made from the posterior end forward. 



Another item to be taken into consideration is that the sper- 

 matozoon may not always be in a perfectly horizontal position 

 on the slide, and hence all parts of it may not be in focus at once. 



Length in n. 22.68 23.76 24.84 25.92 27.00 28.08 29.16 30.24 31.32 32.40 33.48 34.56 35.64 36.72 



FIG. 8. Bimodal curve of variability of chromatic-rod length for 3r. Greater 

 number of spermatozoa around lower mode, M'. 



Length in M. 22.68 23.76 24.84 25.92 27.00 28.08 29.16 30.24 31.32 32.40 33.48 34-56 35-64 36.72 



FIG. 9. Unimodal curve of variability of chromatic-rod length for 3). M" 

 the only mode. 



This may be due to a downward or upward bending or curving 

 of the anterior end of the head, or to a tilting of the entire head, 

 whether curved or straight. To preclude any danger of incorrect 

 measurement all such spermatozoa were recorded separately and 

 only entered in the data with those which were distinctly crooked. 



