lO STUDIES IN SPERMATOGENESIS. 



The centrosome is evidently applied to the nuclear membrane, as in 

 Stenopelmatus , and the middle-piece is developed in connection with 

 it, as in figures 156-157, 154-155, 158-160. The element jc of the 

 spermatids gradually disappears (figs. 150, 159). An acrosome develops 

 at the anterior end, the head condenses and lengthens, and we have the 

 ripe spermatozoon (fig. 161). The tail is very long and is shown only 

 in part. 



Of the forms studied, Blattella alone has many degenerate sperm- 

 atozoa. Some follicles have none, others a number varying perhaps 

 from one-fourth to three-fourths of the whole number. No evidence 

 of degeneracy was detected among the young spermatids up to the 

 stage shown in figures 154-155, where a few like figure 162 were found. 

 Most of the degenerate forms occur among the nearly ripe spermatozoa 

 or in the sperm-ducts. Such are shown in figures 163 to 168. The 

 chromatin is strangely broken up into irregular clumps, and probably 

 no two of these degenerate sperm -heads can be found which are alike. 

 The tails are always imperfect. The distribution and varying num- 

 bers of these degenerate spermatozoa make it impossible to interpret 

 their condition as due to the absence of the accessory chromosome, 

 as Miss Wallace does in the spider. The only probable explanation, 

 it seems to me, is imperfect mitosis. Cases where more or less chro- 

 matin is left behind in the cytoplasm, especially in the first spermato- 

 cyte mitosis, are very common, and such cases as those shown in 

 figures 149 and 150 are not rare. The giant cells, so far as I have 

 been able to trace them, do not develop into spermatozoa. 



The most important points are : 



(i) The presence of the element x in the spermatogonia, closely 

 associated with the nucleolus. 



(2) The uneven number of chromatin elements in the metaphase of 

 spermatogonial divisions. 



(3) The connection of the element x with the spireme up to the 

 stage where the spireme segments to form the bivalent chromosomes. 



(4) The varied character of the tetrads, showing the first spermato- 

 cyte division to be a reducing division in the sense that it separates 

 whole chromosomes. 



(5) The fact that the element x fails to divide in the first maturation 

 division, does divide in the second, but can not be traced beyond the 

 equatorial plate of the latter mitosis. 



(6) The similarity of all the normal spermatids, though one-half of 

 them must contain the element x, the other half not. 



(7) The varying and often large number of degenerate spermatozoa. 



