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THE AMERICAN NATURALIST [Vol. XLII 



daughter nucleus following the mitosis is accompanied by such a 

 central body, or centrosome, with delicate protoplasmic radiations ; 

 the greater number of these daughter nuclei degenerate. The 

 cytoplasm begins to gather around those which survive, and such 

 regions become the egg origins. Each egg origin has then in its 

 interior a nucleus accompanied by a central body with radiations 

 that extend outward in all directions through the cytoplasm. 

 There is finally a cleavage of the cytoplasm between the egg 

 origins and a rounding up of the protoplasm of each to form 

 the egg. 



The central body of Claussen with its radiations is very con- 

 spicuous at certain stages of oogenesis. Davis believed the struc- 

 ture to be analogous to the coenocentrum of the Peronosporales 

 and to be developed in the cytoplasm without genetic relation to 

 the nucleus. Trow described asters associated with the surviving 

 nuclei of the oogonium and believed them to be accompanied by 

 deeply staining material constituting a body called by him an 

 ovoeentrum. The coenocentrum of Davis corresponds to the 

 ovocentrum and egg aster of Trow and to the central body with 

 radiations of Claussen. The views of Claussen are very inter- 

 esting and the theory is logical, but his observations on the cen- 

 tral body are not sufficiently detailed to establish fully his con- 

 clusions. The nuclei of the Saprolegniales and Peronosporales 

 have been studied by a number of competent observers who have 

 failed to find a polar organization. However, these nuclei are 

 small and the problem difficult, and further investigation may 

 establish nuclear polarity in these groups of fungi similar to that 

 in the Ascomycetes as determined by Harper. Should such 

 evidence be forthcoming, the subject of nuclear structure and 

 behavior in the Phycomycetes will take on an entirely new aspect 

 of great significance in the explanation of the processes of 

 gametogenesis and fertilization. 



Claussen finds that the eprgs of Saprolegnia monoica are fer- 

 tilized, thus adding another form to Trow's list of sexual species, 

 and it seems clear that fertilization occurs for a number of 

 species in this group of fungi which is so largely apogamous. 

 There is a single mitosis in the antheridium, with radiations 

 around the central bodies less evident than in the oogonium. 

 The antheridial tubes on entering the oogonium may apply 

 themselves directly to the egg, but more frequently the ends 

 branch and their tips become applied to several eggs. Finally 



