DIMORPHISM OF SPERMATOZOA 619 



with an oil immersion, and the resulting image thrown on the 

 table, even of such a small object as a spermatozoon head, is 

 sufficiently large to admit of measuring round a curve with 

 a pair of compasses. The co-efficient was worked out previously 

 by putting a stage micrometer in the microscope and finding 

 out how many centimetres on the table corresponded to lO/n 

 on the slide. The subsequent calculation was as easy as that 

 necessary when using an ocular micrometer. By this means 

 the unavoidable margin of error in the measurements was 

 very greatly reduced. On one occasion when the drawing 

 apparatus was out of order some measurements were made 

 with the aid of a camera lucida. In both cases extreme 

 dimensions were marked on paper, connected by a line, and the 

 whole number measured afterwards. An 18 Zeiss ocular could 

 be used with the camera lucida, but not with the drawing 

 lantern, owing to the excessive diffusion of light, and so the 

 nett magnification came to about the same in both cases. 



Wodsedalek measured the spermatozoa in testis sections 

 by the camera-lucida method, and Zeleny and Faust used 

 smear slides with the ocular micrometer. It will be seen, 

 therefore, that the method described above is a combination 

 of the two, and it was found to be the most satisfactory. The 

 error involved by the use of the ocular micrometer is avoided, 

 as is the possibility of getting immature spermatozoa on the 

 slide. 



As the whole value of the work depends on the degree of 

 accuracy which can be achieved, the following remarks may 

 not be out of place. Three sources of error arise : 



(a) Distortion of the spermatozoa during fixing and preparing, 

 (fo) The personal factor in measuring, 

 (c) The un&.voidable error in measuring. 



With regard to the first point, general shrinkage of the 

 spermatozoon head must almost inevitably occur ; but only one 

 slide was used for each set of measurements, and no attempt 

 has been made to mix measurements from different slides. 

 As the spermatozoa on one slide would all be affected in the 



