Cytology of a neiv variety of A chly a americana. 133 
continuous observation, in part under the microscope ; to 
find methods of fixing, imbedding, and staining, so as to 
secure well-stained serial sections of the organs which were 
to be submitted to detailed critical study ; and finally to 
bring to bear upon the microscopic examination of the 
preparations the finest optical apparatus and the best technical 
skill available. 
Prof. Hartog, no mean authority, states concerning one 
of the stages : — £ the study of the nuclei and their behaviour 
at this period becomes enormously difficult ; and it is only 
possible under the best possible conditions of preservation, 
staining, and microscopic apparatus.’ My experience leads 
me to endorse this view, and it may be remembered that 
Dangeard completely failed to find the nuclei in certain stages. 
It seemed clear, too, that work done on mixtures of species, 
and especially mixtures of genera, would be certain to lead 
to serious error. Accordingly it was decided to work with 
a single species of Achlya and to keep four definite points 
in view throughout ; viz. : (1) the structure of the nucleus and 
especially its behaviour during karyokinesis, (2) the fate of 
the supernumerary nuclei in the oogonia during the develop- 
ment of the oospores, (3) the actual method by which 
fertilization is effected, and (4) the behaviour of the nucleus 
during the germination of the oospores. 
A beginning was made in the summer of 1897 by Miss 
Dawson, who collected in the neighbourhood of Cardiff, 
and cultivated for a generation or two, a species of Achlya , 
which formed numerous sexual organs and was apparently 
very suitable for detailed cytological study. She adopted 
the methods of preparation which I had found most suitable 
in the study of Saprolegnia , but failed in the short time at 
her disposal — two months — to secure any satisfactory results 
in cytology. 
In the autumn of the same year I commenced to work at 
this material myself. Fresh cultures were made in August, 
and upon these a preliminary study of the fresh material 
was instituted. Finally, about a dozen different methods 
