STUDIES ON CHROMOSOMES. 249 



cytoplasm of the transforming spermatic! and left behind. It is 

 not easy actually to establish this, but such would be the infer- 

 ence based upon the many non-nucleated bits of cytoplasm 

 scattered among the spermatids, together with the fact that 

 lobes of cytoplasm may be seen projecting from many of the 

 transforming cells. On the other hand it is possible that these 

 bits are cytoplasmic fragments from degenerating speimatids. 



SPERMATOZOA. 



In my earlier paper I came to the conclusion that there were 

 two classes of spermatozoa. My present work shows that I was 

 probably in error on this point. My earlier work was based on 

 measurements of the heads of 100 spermatozoa as they existed 

 in smears of the testicular material itself. While no curve was 

 plotted my older notes show that I obtained two means standing 

 in about the relative ratios of 8 to 10. What would have made 

 the 8|, 9, and 9^ groups, however, would afford but slight 

 depression in a bi-modal curve. Furthermore, when later I 

 came to measuring spermatozoa from the vas defer ens, as I 

 should have done for the eailier work, I found that the sperma- 

 tozoa taken from testicular smears show a larger size and a far 

 greater range of fluctuation in length of head than do those 

 from the vas deferens. This means that doubtless many of 

 those I measured in my earlier work had not yet completed their 

 transformation and settled down to their final size. 



The present measurements were made in four series based 

 upon the length of head of spermatozoa taken from the vas def- 

 erens of two Plymouth Rock fowls. Two of the series, one 

 from each fowl, including measurements of 500 and 515 sperma- 

 tozoa respectively, I myself made. The other two, each con- 

 sisting of measurements of 100 spermatozoa, were made as a 

 control by an instructor (Dr. Elizabeth A. Smith), who is ac- 

 customed to doing cytological work but who was wholly in the 

 dark as to what result had been obtained in my own measure- 

 ments. The instructor worked with material from the same 

 fowls but on different slides from the ones I used. The details 

 are shown in Text-figure 2. 



It is by no means an easy task to obtain such measurements 



