296 E. C. FAUST. 



The total of all spermatozoa, curved, crooked and tilted, which 

 were not measured amounted to three to five per cent, of the 

 numbers measured. Had this group been all of a critical length 

 they would not have been sufficient in a single case to change the 

 fundamental character of the curve of variability. An example 

 of such a "curved" sperm-head is shown in Fig. I, c. 



A question arose as to how many spermatozoa must be meas- 

 ured before the curve is fairly constant and dependable. It has 

 been observed that with one hundred fifty or two hundred indi- 

 viduals the main features of the curve are outlined; that the 

 curve fluctuates in its details up to three hundred individuals; 

 that four hundred individuals are enough to give a curve of 

 variability which is accurate and dependable. Even a measure- 

 ment of seven hundred ten individuals, which was made in one 

 case (number ir), failed to change the character of the curve 

 from that secured for the first four hundred of the seven hundred 

 ten individuals. 



In addition to these precautions, several other checks were 

 made in measurement. One preparation, number ir, was 

 measured three times with three different magnifications; the 

 curves for all three measurements were similar. All measure- 

 ments were made with the writer's same eye, but were checked 

 by other research students in the laboratory. Finally, only the 

 best of light was used while the measurements were being made. 



III. DATA OBTAINED. 



The data presented were obtained from eight smear prepara- 

 tions taken from four pairs of testes, fixed and stained by the 

 osmic-Delafield method described above. These preparations 

 are designated as I right (ir) and I left (il), 2 right (2r) and 

 2 left (2!), 3 right (3r) and 3 left (3!), 4 right (4r) and 4 left (4!). 

 Taken as a whole the measurements show very clearly that there 

 is a distinct size dimorphism in the spermatozoa. Individual 

 testes, however, differ considerably from each other in details. 



Preparations ir and il. These spermatozoa when examined 

 in Ringer's solution were very active. From one thousand to 

 two thousand individuals were present on each slide preparation, 

 comprising the total number of spermatozoa from each testis. 



