438 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



bodies, as in the basidium, which stand intermediate in size 

 between centrosomes and centrospheres and are probably only 

 called the former because they are very distinct in outline. 



Centrospheres in Fucus (Fig. 3 d, Section I), Corallina (Fig. 

 4 b) and Pellia (Fig. 3 e. Section I, Fig. 4 c) are formed de novo 

 for each mitosis by an accumulation of kinoplasm at the poles of 

 the elongating nucleus. The centrospheres in the ascus divide 

 before each of the three successive mitoses and finally remain, 

 one for each nucleus, to instigate the peculiar process of free 

 cell formation characteristic of the ascus. Centrospheres are 

 frequently the centers of asters which, however, are usually not 

 as sharply defined as those with centrosomes, possibly because 

 the fibers are not grouped with the same degree of symmetry as 

 is shown around controsomes. 



Spindle fibers from centrospheres develop in precisely the 

 same manner as from centrosomes, i. e. by the growth of the 

 fibrillse into the nuclear cavity through the dissolving nuclear 

 membrane. The activity is well shown in the oogonium of 

 Fucus, and Farmer ('98, p. 638) believes "that the intranuclear 

 part of the spindle is differentiated out of nuclear material that 

 is unused for chromosome formation." The entrance of spindle 

 fibers from centrospheres at the ends of a nucleus has been 

 observed by myself in Corallina, Fig. 4 b (Davis, '98). The 

 germinating spores of Pellia, Fig. 4 c (Davis, :oi. Chamberlain, 

 :o3) furnish especially good illustrations of the entrance of spin- 

 dle fibers into the nuclear cavity and the development of the 

 spindle in this form is coincident with the dissolution of the 

 nucleus vifhich, according to Strasburger's theory ('95), indicates 

 that the latter structure contributes material for the growth of 

 spindle fibers. 



In connection with the centrosphere mention should be made 

 of the blepharoplasts of the cycads and Ginko which are remark- 

 able bodies with radiating fibers. They have been considered 

 by some as asters with centrosomes, but it is known that they 

 take no part in spindle formation or other mitotic phenomena in 

 these forms, and consequently need not be considered at this 

 time. They will be treated in some detail in the account of the 

 sperm (Section III). 



