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 former, 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 
odgonium 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, and 
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 imparted 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 odgonium 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- 
