^584 THE AMERICAN NATURALIST. [VOL. XXXVIII. 



evident that final judgment cannot be passed until certain ques- 

 tions of fact are established by reinvestigations. Shaw and 

 Belajeff cannot both be wholly correct in their observations and 

 interpretations and much depends upon the exactness of future 

 studies upon Marsilia, other pteridophytes, and in the bryo- 

 phytes. The problems are also related to the processes of 

 zoospore formation among the thallophytes. 



With respect to the bryophytes Ikeno ( : 03) has recently 

 published an account of spermatogenesis in Marchantia poly- 

 morpJia. He reports for the mitoses in the antheridium, prelim- 

 inary to the differentiation of the sperm mother-cells, that a 

 centrosome appears at the side of each nucleus and divides, the 

 two daughter bodies passing to opposite sides of the nucleus and 

 becoming the poles of the spindle. He gives evidence that the 

 daughter centrosomes sometimes divide again when at the poles 

 of the spindle in anaphase. The centrosome cannot be found 

 at the side of the daughter nucleus after the mitosis is com- 

 pleted but it appears when the nucleus is ready for the next divi- 

 sion. Ikeno's explanation of the reappearance of the centrosome 

 is unusual. He believes that the centrosome is formed within 

 the interior of each nucleus as a deeply staining body among the 

 linin threads. This body moves to the nuclear membrane and 

 is thrust out into the cytoplasm through a protuberance from 

 the nucleus. It then lies outside of the nucleus and becomes 

 the functioning centrosome, dividing to form two centrosomes 

 that separate to preside over the poles of the spindle. After 

 the final mitoses in the spermatogeneous tissue the centrosomes 

 remain to become the blepharoplasts of the sperms. Each 

 blepharoplast passes to the plasma membrane of its sperm cell 

 and develops two cilia. There is formed at this time another 

 deeply staining body in the cytoplasm considered by Ikeno equiv- 

 alent to a " Nebenkorper." The nucleus begins to elongate 

 and the "Nebenkorper" takes a position between it and the 

 blepharoplast and in this manner the much attenuated sperm is 

 organized from the mother-cell. 



Ikeno considers the blepharoplast of Marchantia to be actu- 

 ally a centrosome as shown by its behavior during mitosis. His 

 account therefore in the main supports Belajeff 's interpretation 



