706 AQUATIC PHYCOMYCETES 



disposed oil droplets in the ooplasm combine to form a number of large 

 refractive globules. These, as the ripening of the egg progresses, may 

 come to occupy a central position in the oogonium. Both Lagerheim and 

 Laibach have shown that the egg is uninucleate, and that the nucleus 

 ultimately attains a terminal position in the oogonium (Fig. 49 H-K, 

 p. 704). 



Apparently fertilization is possible only after the egg has reached the 

 proper stage of development. It was frequently observed that anthero- 

 zoids creeping over immature eggs could not fertilize them. Often, too, 

 they seemed unable to fertilize ova which, by their appearance, were 

 fully mature. Whether this was due to the fact that the eggs were only 

 seemingly mature or to the circumstance that the antherozoids from 

 androgynous antheridia were unable to fertilize their own oosphere is 

 in need of further investigation. The latter explanation does not seem to 

 suffice in all instances, however, for numerous examples of self-fertili- 

 zation may be found. 



When an antherozoid approaches the apex of an oogonium the 

 peripheral collar of the wall of the latter, until then contiguous with the 

 papilla (Fig. 50 B, p. 708), dilates slightly (Fig. 50 C-D). The sperm 

 resting on the mucilaginous papilla, which seems to be an integral part 

 of the ooplasm, is immediately engulfed (Fig. 50 E-F), and both sperm 

 and papilla become relatively indistinguishable from the egg. The 

 flagellum of the sperm may protrude for a few moments, but it, too, is 

 finally absorbed. After fertilization, the egg, which has previously 

 become more compact and has moved toward the apex of the oogonium, 

 retreats slightly and remains motionless for from three to five minutes. 

 It then expands, and in some species there is initiated a gradual evacua- 

 tion from the oogonium (Fig. 50 H-J). The time required for this 

 process varies, but it usually takes at least two minutes. The wall of 

 the oogonium is again dilated as the egg commences to emerge. In rare 

 instances the protoplasm of the antherozoid may still be distinguishable 

 at this time. 



Outside, the egg remains attached by a narrow hyaline collar to the 

 mouth of the oogonium. A pellicle soon forms around it, which grad- 

 ually thickens and on which in most species there appear regularly 

 placed protuberances (Fig. 50 J-K). These grow in size and become 



