﻿1 903 J OOGENESIS IN SAPROLEGNIA 241 



trum is really the key to many of the problems of oogenesis in 

 Saprolegnia. 



The coenocentrum varies in its minute structure with differ- 

 ent periods of oogenesis. It is at first a small body composed 

 ^ of several granules imbedded in dense material, from which a 

 number of delicate fibrils radiate into the surrounding cyto- 

 plasm. The structure stains deeply and resembles an aster. 

 After the eggs are fully formed the rays disappear and the coeno- 

 centrum grows larger, takes on a spherical form, and resembles 

 a globule of oil or fat. It finally dissolves, sometimes with frag- 

 mentation, and completely disappears, in the older eggs. The 

 coenocentrum is thus a structure peculiar to that period of 

 oogenesis characterized by nuclear degeneration and the seg- 

 mentation of the protoplasm to form the eggs. It bears a most 

 important relation to these tw^o events, which are the most diffi- 

 cult to study in the entire process of oogenesis. 



We must begin with the first appearance of the coenocentra. 

 These structures may always be found before the differentiation 

 of the ^^g origins, at the time when the oogonium is filled with 

 ,^ degenerating nuclei. The latter lie scattered through the cyto- 

 plasm {-figs, j^, 75), and exhibit varying degress of dissolution. 

 The young coenocentra are always found in the densest regions 

 of the protoplasm, portions destined to become tgg origins, such 

 as are shown in figs. 14 and 75. They are very small at first 

 and would scarcely be noticed except for the radiating fibrils 

 that mark their position. They increase in size as the c^^ ori- 

 gins take more definite form (Jig. 16) . 



An examination of figs. 14-16 shows at the side of each 

 coenocentrum a small nucleus. This structure Is very small at 

 early periods of oogenesis {figs. 14, /j), and scarcely more clear 

 than many of the degenerating nuclei in the neighborhood; but 

 as oogenesis proceeds the nucleus accompanying the coenocen- 

 trum growls larger and increases greatly in staining material {fig. 

 r6). When the eggs are fully formed, this nucleus is many 

 times larger than at the first appearance of the coenocentrum, as 

 n^ay be seen by comparing /^.y. iy^2i with figs. 14 and 75, which 

 are all magnified 1,000 diameters. One would hardly think it 



