ZOOLOGY: ZELENY AND FAUST 
91 
DIMORPHISM IN SIZE OF SPERMATOZOA AND ITS RELATION 
TO THE CHROMOSOMES 
By Charles Zeleny and E. C. Faust 
ZOOLOGICAL LABORATORY. UNIVERSITY OF ILUNOIS 
Presented to the Academy, December 4, 1914 
Cytological studies have shown that in the maturation divisions of 
a large number of species of animals the cells which are to give rise to 
the spermatozoa are of two kinds, differing from each other in the 
nature of their chromatin content. The resulting spermatozoa there- 
fore are assumed to be likewise of two kinds. A large mass of indirect 
evidence makes it highly probable that eggs fertilized by one of these 
produce only males and those fertilized by the other only females. 
3^9 3W. 320 3Z3 33ii 33.6 342 34.7 353 358 36.4 369 375 38.0 38.6 39.1 397 402 408 413 4].3 424 43jO 436 441 4A6 
Head lengths of spermatozoa m rnicrops 
Explanation of Figure 
Frequency distribution of head-lengths of 444 spermatozoa from right testis of Musca 
domestica. 
Value in microns 30.9 31.4 32.0 32.5 33.1 33.6 34.2 34.7 35.3 35.8 36.4 36.9 37.5 
Frequency 1 3 5 6 11 9 12 16 20 39 38 33 20 
38.0 38.6 19.1 39.7 40.2 40.8 41.3 41.9 42.4 43.0 43.5 44.1 44.6 
40 50 39 33 27 17 14 11 5 1 1 2 1 
Direct experimental test of this hypothesis has not been made because 
recognition of the difference has been confined to the immature stages. 
It is therefore of importance to see if the two kinds can be made out 
among the completed functional spermatozoa. The present studies 
were planned with a view to such a determination. If there is a differ- 
erence in the amount of chromatin received by the two kinds of sper- 
matids it is natural to expect a corresponding difference of size in the 
heads of the completed spermatozoa since these are made up almost - 
wholly of chromatin material. 
