DIMORPHISM OF SPERMATOZOA 621 



It will be seen that the range of the variation in the three 

 measurements is only 0-05 ju- or -^Q^l. 



The second manner of testing accuracy consisting in measur- 

 ing the same spermatozoon several times under the same 

 magnification, and the results gave a range of variation in six 

 measurements of O-lOjtt or .^^q/x. Both these margins of error 

 are very much smaller than the least fraction of /x. usually 

 dealt with. 



I should like to take this opportunity of acknowdedging my 

 great obligation to Mr. J. T. Wadsworth for his invaluable 

 assistance in the technique of this work. 



Spermatozoa of Man, Eat, Cat, and Mouse. 



Von Winiwarter (4) has described chromosome dimorphism 

 of human spermatozoa according to the presence or absence 

 of an unpaired accessory. In my material, measurement of 

 the head lengths was found to give the following results : 



Table I. Frequency of Head Lengths or Spermatozoa 

 OF Man. 



In the case of the rat Allen (1) has demonstrated an accessory 

 chromosome in spermatogenesis, the spermatozoa having 

 eighteen or nineteen chromosomes. The dimorphism again 

 appears to communicate itself to the head sizes of the sperma- 

 tozoa, for dimorphism was found in the head lengths of the 

 spermatozoa of the rat. The frequency polygon given below 

 (Text-fig. 2) was made from measurements of the head lengths 

 ( X 4,000) of 155 spermatozoa. 



