ACHLYA AND SAPROLEGNIA. 103 



De Bary, while Trow brings forward fresh evidence in behalf of a real 

 fecundation. The rapid strides made in our knowledge of cytology by 

 the application of better methods of technique and skill in manipula- 

 tion has not only brought to light fresh questions of inquiry, but has 

 made possible also new points of view. Consequently, the observers 

 last mentioned find themselves differing not merely upon the old ques- 

 tion, but upon others of deep significance in connection with the sexual 

 process. 



Following each of the two publications of Trow ('95, '99) has 

 appeared a criticism by Hartog, in which he calls into question the 

 statements of the formej, without, however, submitting the results of 

 any new observations. As will be shown later, the chief difference of 

 opinion between Hartog and Trow, apart from the main contention, 

 lies in the behavior of the nuclei during the development of the 

 oogonium and the differentiation of the eggs. Hartog finds that, 

 during the development of the oogonium, the nuclei fuse in groups to 

 form the functional nuclei, one of which is present in each egg, ancl 

 concludes with De Bary that no fecundation takes place. Trow finds 

 that a certain number of the nuclei remains functional one for each 

 egg-cell developed and that in certain species, as Saprolegnia dioica 

 and Achlya americana, a real sexual process exists. Trow has not 

 demonstrated beyond all question that fecundation does take place even 

 in the species that seems to furnish the best evidence, but, on account 

 of the superior methods used, we are nevertheless justified in believing 

 that his results afford the strongest proof that has ever been advanced 

 in favor of a sexual process, and stronger than all of his recent oppo- 

 nents have produced to the contrary. 



Since the behavior of the nuclei is of prime importance in the differ- 

 entiation of the sexual elements, and as this is one of the chief points 

 in controversy, a somewhat detailed account of the behavior of the 

 nuclei during the development of the oogonium and the differentiation 

 of the egg-cells will lead the reader to a clearer understanding of the 

 questions in debate. 



The young oogonium arises as a globular enlargement at the end of 

 a filament, into which flows dense granular cytoplasm together with 

 a number of nuclei. With an increase in size a large vacuole appears 

 in the base of the oogonium, and this vacuole is continuous with a 

 cylindrical vacuole in the filament (Fig. 37, A) . With further growth, 

 which is rapid, the vacuole becomes very large and the cytoplasm is 

 confined to a dense wall-layer. During this process a transverse wall 

 is formed delimiting the oogonium from the filament. The nuclei, 

 which are now distributed in the layer of cytoplasm, divide karyo- 



