430 MARCUS M. HARTOG. 



finance of the lines of preliminary division. They are the 

 optical expression of thinnings of this parietal layer 

 between prominences rounded towards the vacuole. 

 These prominences enlarge, and the protoplasm aggregates 

 more and more in them as they become nearly hemispherical ; 

 and the intermediate protoplasm becomes thinner and thinner, 

 so as to give the impression of clear spaces in surface view ; but 

 in optical section it is easy to assure oneself that the proto- 

 plasm lining the sporange wall is everywhere continuous and 

 closely applied thereto. Careful focussing everywhere shows 

 the continuity of the clear bands and the vacuole. The 

 granules which first marked out the lines of demarcation in 

 Achlya do not disappear j they form a layer at the edge and 

 over the free surface of each hemispherical prominence, and 

 are seen as lines bounding it in plan and in optical section. 



When the sporange of Achlya is normal the central vacuole 

 is replaced by several, owing to the abundance of protoplasm ; 

 and these in the first stage become converted into a continuous 

 system of lacunae. The inner masses of protoplasm are all 

 connected by thinner bands. 



In the narrower sporanges ofLeptomitus there is no room 

 for a double row of prominences ; hence in section they pro- 

 ject alternately, and the central vacuole becomes zigzag. 

 Here it is easy to see that the lines or bands of the preliminary 

 division are merely thinnings of the protoplasm.^ 



In the undetermined Saprolegnia the central vacuole per- 

 sists, communicating, I think, with a lacunar system of spaces 

 in the thick parietal layer of protoplasm, which includes several 

 layers of prominences (or rather aggregations of protoplasm). 



The homogeneous stage consists essentially in the swelling 

 up of the protoplasm and the loss of its resistance to 

 osmosis. On examining a normal sporange of Achlya, and 

 carefully focussing a lacuna with a high power (Zeiss E ^" for 

 instance), "we see at the onset of this stage that the margins of 

 the lacuna advance and meet from the angles inwards until the 

 space disappears completely, much in the same way as the con- 

 ' As indeed figured by Biisgen (op. cit., T. xii, figs. 11, 12). 



