BLA.CKMAN: THE SPERMATOGENESIS OF SCOLOPENDlIA. 119 



The appearances are very much alike in both cases, and in each this 

 stage is followed by an apparent growth of the nucleus. However, 1 

 believe that the acrosome is in reality derived from the archoplasm, as 

 he concludes; but I do not believe the structure described as the sphere 

 in his Figure 316, A, is such. At least in Scolopendra tie fundaineuts 

 of the acrosome appear much later. 



Collin and P. et M. Bouin do not trace the origin of the acrosome, 

 but describe its appearance at the anterior end of the nucleus at the 

 time when this is beginning to elongate. It is improbable that Geophi- 

 lus differs from other chilopods in this matter. 



Perhaps the most remarkable fact in regard to the acrosome in Scolo- 

 pendra is its immense size as compared with the similar structure in 

 other animals. It is indeed surprising that there should be such a dif- 

 ference in this regard between Scolopendra and animals so closely related 

 to it as Lithobius and Geophilus. Yet from my own observations upon 

 the spermatids of these forms, I am certain that such differences exist. 

 I have studied only maturing spermatozoa as they occur in the still de- 

 veloping testis, and it is possible that they may mature still further and 

 lose at least a portion of the acrosome. Yet this would not explain the 

 differences existing in an earlier stage, for at all times the acrosome in 

 Scolopendra is large and conspicuous, whereas in Lithobius it is always 

 small. It is possible that some structural condition may exist in the 

 eggs of Scolopendra which necessitates the enormous development of the 

 acrosome. 



V- Summary. 



After the last spermatogonial mitosis the small cells resulting enter 

 upon a period of extraoi'dinary growth, by which their diameter is in- 

 creased from five to ten times. Tliese growing cells are early divisible as 

 regard* size into tiro classes. Those of the larger type remain united in 

 pairs during the growth period by means of the persisting interzonal fila- 

 ments, and lie in uncrowded region* of the testis, where they are surrounded 

 by a plentiful supply of food material. The cells of the smaller type do 

 not remain thus united, and are so crowded that a rich supply of nutri- 

 ment is not possible. 



At the completion of the growth period — "the vesicle stage " — 

 the spermatocytes bear a strong resemblance to egg cells during the 

 germinative-vesicle stage, and this is especially true of the larger type of 

 cells, which hare been surrounded by conditions similar to those of the 

 growing egg. 



