1914] SHARP— SPERMATOGENESIS IN MARSILIA 427 



lo the present writer it seems clear that we are here dealing 

 with an organ which is gradually passing out of the life history. 

 The farther we pass back from the last spermatogenous mitosis the 

 more indefinite its behavior becomes. The centrosome appearing 

 in the third mitosis is intimately concerned in the formation of the 

 achromatic figure for the fourth mitosis, and before the latter is 

 complete the centrosome has already begun to undergo the peculiar 

 transformation of the blepharoplast. The centrosome appearing 

 at the second mitosis later divides, but only occasionally goes 

 farther. In the first mitosis there seems to be still an abortive 

 start in the formation of a centrosome at anaphase (fig. 15), but 

 no definite body is organized. Even in the earlier mitoses of the 

 male gametophyte a system of rays suggests the presence of a 

 dynamic center at each spindle pole, though no centrosome is 

 present (fig. 4). 



These considerations, taken together wi 



centrosomes 



number 



in which they are limited to the last mitosis (Equisetum, Nephro- 

 dium, cycads), have only served to strengthen our formerly ex- 

 pressed opinion that centrosomes have been partially or wholly 

 eliminated from the early spermatogenous cells, and are retained in 

 so many forms only at the end of the series because of the very 

 important biological function they there perform — the bearing of 

 cilia. They are finally lost altogether when the change from motile 

 to non-motile sperms occurs. Just such a progression as this is 

 seen in passing upward through the bryophytes, pteridophytes, 



the 



gymno sperms, and Marsilia 



A feature of special interest is the degeneration of the Marsilia 

 centrosome just before the third spermatogenous mitosis, and the 

 formation of a new one at each spindle pole. This was also reported 

 by Shaw (7), while Belajeff (3) thought there was no break in its 

 continuity after the time of its first appearance. As stated in the 

 description, our material shows at this point some variability, and 

 it is of a sort which tends to reconcile the two earlier accounts. 

 In the majority of cases degeneration begins directly after the 



