198 KANSAS UNIVERSITY SCIENCE BULLETIN. 



very often lie in another section, where it would not be possible 

 to be sure of its relations. I am convinced from these counts 

 that seventeen is the reduced number in the first spermatocyte, 

 sixteen of the elements being ordinary chromosomes, the other 

 one being the accessory chromosome which has come over un- 

 altered from the spermatogonia. This coincides with the theo- 

 retically expected number, deduced from the independently 

 determined number of spermatogonial elements. 



In view of the divergences found in insect spermatogenesis, 

 the established theory that the reduced number of chromo- 

 somes is exactly half the normal or somatic number is not a 

 strictly accurate one, for in this case the reduction is from 

 thirty-three to seventeen. Similar instances may be found in 

 the forms investigated by Montgomery and de Sinety. 



When we come to consider the second spermatocytes, sperma- 

 tids, and spermatozoa, it is necessary to divide them into two 

 classes, because of the unequal apportionment of the accessory 

 chromosome consequent upon its remaining undivided in the 

 first spermatocyte mitosis. There are formed, accordingly, two 

 numerically equal classes of second spermatocytes — those con- 

 taining sixteen chromosomes plus the accessory chromosome, 

 and those with merely the sixteen chromosomes. The mem- 

 bers of each of these classes divide and double their kind, form- 

 ing spermatids marked as were the second spermatocytes — one 

 class with seventeen chromatic elements, and the other with 

 sixteen. From these, by the usual transformations, are derived 

 the mature male elements, which are thus of two distinct kinds. 



(/) Spermatids. 

 The limits set to this paper preclude anything more than 

 passing mention of the spermatids. As stated above, cells at 

 this stage of development are of two classes, depending upon 

 the presence or absence of the accessory chromosome. The dis- 

 tinction thus set up continues to exist visibly far through the 

 transformation stages of the spermatid, by reason of the per- 

 sisting independence of the accessory chromosome. Of the 

 dual nature of the spermatids I was very early convinced, be- 

 cause the accessory chromosome is so strikingly displayed by 

 the nuclei in which it exists that it is impossible to overlook 

 its absence in a large proportion of the cells. As to the 



