1909] YAMANOUCHI— MITOSIS IN FUCUS 179 



rise by simultaneous division to sixteen nuclei (fig. 37). The fifth 

 division follows at once in each of these sixteen nuclei, resulting in 

 the formation of thirty-two nuclei (fig. 38). These simultaneous 

 mitoses take place with only short resting periods between, and 

 precisely the same as the second mitosis. The centrosome is most 

 brilliant at the first mitosis and gradually becomes fainter in the 

 successive divisions. The number of chromosomes in early meta- 

 phase (figs. 34a, 37a, 38a) and late anaphase (fig. 36a) of these 

 mitoses is 32. 



The formation of partition walls in the antheridium begins to 

 take place at the 32-nucleate stage. Up to this stage, the nuclei of 

 the antheridium are free, but finally in telophase of the fifth mitosis, 

 with the disappearance of the central spindle in each mitotic figure, 

 there could be seen in the neutral region between any two nuclei the 

 faint manifestation of a protoplasmic plate formed by the transverse 

 walls of fine alveoli becoming perceptibly thicker and arranging 

 themselves in such a way as to appear as an uneven or somewhat 

 zigzag line in section. The unevenly continuous walls of the alveolar 

 lamellae grow gradually thicker, and soon uniform plates are laid 

 down simultaneously, so that the antheridium is divided into 32 cells. 



The nuclei in these cells of the antheridium undergo one more 

 mitosis, the sixth, which results in 64 nuclei (fig. 39)- Thirty-two 

 chromosomes are present at this mitosis (fig. 39a) . This last division 

 is also accompanied by the laying down of thin protoplasmic parti- 

 tion walls, so that the antheridium now contains 64 cells, which are 

 spermatids or sperm mother cells. 



The nuclei in the spermatids undergo a peculiar modification, and 

 *tfn an accompanying change of cytoplasm surrounding the nucleus, 

 th ere is produced a sperm with two cilia. The details of the events 

 *hich occur in the antheridium following the 32-celled stage, as well 

 fs the development of the sperm from the spermatid, will be treated 



in a 



separate paper which will be published later. 



MITOSES IN OOGONIA 



It is well known that oogonia in Fucus develop from the wall cells 



ot the conceptacle. The wall cell puts forth a papilla which divides 



two cell s, an oogonium and its stalk. The oogonium enlarges 



