DIMORPHISM IN SPERMATOZOA OF ANASA. 



291 



sheath is two to three times as thick as the chromatic rod. It 

 extends 2n to 3/z anterior to the anterior end of the chromatic 

 rod, and is continuous posteriorly with the sheath of the axial 

 filament. Considerable observation has shown that the fre- 

 quency curve for chromatic rod length does not differ from the 



Frequency. 



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 



FIG. 2. Bimodal curve of variability of chromatic-rod length for ir. Greater 

 number of spermatozoa grouped around the upper mode,[M". 



Frequency. 



Length in n. 22.68 23.76 24.84 25.92 27.00 28.08 29.16 30.24 3i.32 T 32.4O 33.48 34.56 35.64 



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

 number of spermatozoa grouped around the lower mode, M'. 



curve for the entire head. Unlike the adult spermatozoa 

 described by Paulmier ('99) and Stevens ('05), the author's 

 preparations show a distinct region of cytoplasm around the 

 chromatic rod, and fail to demonstrate that the sheath is entirely, 

 or even mostly "used as food material for the growth of the tail 

 sheath," as Paulmier described it (p. 254; also Figs. 56 and 57). 

 The author's haematoxylin preparations show no acrosome or 



