DIMORPHISM IX SPERMATOZOA OF AXASA. 289 



tions, the results obtained from them have not been included 

 in the data. 



In the aceto-carmine preparations it was found that drawing 

 off the excess stain by a bit of filter paper as recommended, 

 carried along with it many spermatozoa. In fact, preliminary 

 measurements of such preparations showed a prevalence of 

 larger spermatozoa on the side toward which the drawing was 

 being made. Precautions were taken to eliminate this fault by 

 fixing the spermatozoa to the slide with a thin film of albumen 

 fixative. Also osmic fumes were used in preference to a liquid 

 killing agent and Delafield's hsematoxylin, instead of some more 

 complicated stain, in order that all the spermatozoa might be 

 preserved. This osmic-hsematoxylin combination has been 

 found particularly effective in producing straight spermatozoa 

 with well-marked chromatic elements. In the preparations 

 from which data were compiled from ninety-five to ninety-seven 

 per cent, of the spermatozoa were sufficiently straight for meas- 

 urement. 



(2) Error Due to Immaturity. When preliminary mounts were 

 made about the first of October, 1912, the material was found to 

 be too immature for the purpose of this work. All stages in 

 spermatogenesis were present from the spermatogonium to the 

 young spermatids, but no adult spermatozoa were found. 



One of the problems confronting the writer in determining 

 suitable preparations for study was the recognition of a truly 

 mature spermatozoon. In general, the attenuated character of 

 the head, with the chromatic rod (nuclear element) extending 

 almost its entire length, is sufficient for the recognition of a 

 mature spermatozoon. On that basis all preparations w r here 

 more than five per cent, of the individuals were immature were 

 discarded. In order to satisfy himself more fully of the maturity 

 of the individuals measured, the author examined all of them in 

 Ringer's solution, which demonstrated their motility. In this 

 fluid the developing spermatids and immature spermatozoa were 

 quiet, while the fully ripe spermatozoa were active for a con- 

 siderable length of time. However, motility is not to be taken 

 as a general criterion of maturity. In the house-fly, Musca 

 domestica, for example, immature forms are motile. Again, these 



