DIMORPHISM IN SPERMATOZOA OF ANASA. 



293 



matic material of the normal forms. Smith's "giant sper- 

 matozoa" of hybrid pigeons, which are twice the normal length, 

 do not appear to belong to this category. In a few cases the 

 author has observed two mature chromatic rods of normal length 

 within a single cytoplasmic membrane. Evidently these were 

 cases where the chromatic elements had divided normally, but 



Length in M. 22.68 23.76 24.84 25.92 27.00 28.08 20.16 30.24 31.32 32.40 33.48 34.56 35.64 35.72 

 FIG. 5. Bimodal curve of variability of chromatic-rod length for 2r. Greater 

 number of spermatozoa around the upper mode, M". 



Frequency. 



45 

 40 



35 

 30 

 25 

 20 

 IS 

 10 



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. 6. Bimodal curve of variability of chromatic-rod length for 2!. Greater 

 number of spermatozoa around the lower mode, M'. 



where the cytoplasm had failed to divide, so that the two chro- 

 matic elements had developed together side by side within the 

 same sheath. It is interesting to note that such "twin" sper- 

 matozoa are always of different lengths, varying from 1.5,11 to 3/1 

 from each other. "Giant spermatozoa" of this same type have 

 been observed by the author in smear preparations of the house- 

 fly, Musca domestica. 



