t^'^i\w0ftf^ %W-es m Spirogyx-a. 293 



cl^rly. detected surrounding greea contents (PL IX. fig. &«»);/ j^: 

 call these cells spore-motlier-cells. They soon increase in size, 

 their membrane separating itself from the contents, and expand- 

 ing into a largeish hollow vesicle. The contents at the same time 

 acquire a yellowish or yellow-brown colour, and separate into a 

 central, denser, yellow-brown nucleus, and a finely granular mu- 

 cilage, which surrounds the nucleus and does not entirely fill the 

 space between it and the membrane (PL IX. fig. 8 b, c, d, e). 

 This finely granular mucilage then becomes balled together, in 

 the space between the yellow nucleus and the surrounding mem- 

 brane, into a single large corpuscle exhibiting a sharply defined 

 outline, and appearing as a transparent vesicle with finely granular 

 contents (fig. 8/,/). The new cell thus formed pushes the 

 brown body, as the figures show, out of its central position, 

 against the wall of the parent-cell or the spore-mother-cell. The 

 pressure of these two bodies causes the rupture of the membrane 

 of the spore-mother-cell : the transparent cell emerges and moves 

 about independently and freely in the filament-cell in the man- 

 ner of the zoospores. 



The expelled zoospores are small elliptical cells ; seen from the 

 side they appear longish (fig. 8 g), from above, round (fig. 8 h). 

 Their aspect resembles that of the moving spores of Achlya pro- 

 lifera more than of any others. Their movement is much slower 

 than that of other zoospores, and is further distinguished by the 

 fact, that in advancing they do not make a complete revolution 

 round their longitudinal axis, but merely slight oscillations to 

 the right and left. In moving about they traverse the cavity of 

 the filament-cells in all directions, mostly gliding onwards along 

 the wall, as if, as it were, seeking an orifice whereby to escape ; 

 but notwithstanding that I observed very many of these moving 

 cells for long-continued periods, I never saw them emerge from 

 the filament-cells in which they had been produced, since no 

 orifice was ever formed in the eve)ywhe)-e closed filament-cells. 

 That these cells possess locomotion-threads (cilia) is certain; I 

 could often detect them in vibration with the greatest clearness ; 

 but as I remained in uncertainty as to the number of vibrating 

 threads, I have omitted them altogether in the drawing. I think 

 it most probable that they have one single thread at the ante- 

 rior extremity ; yet in certain cases it appeared as if they bore a 

 crown of several threads. 



i' After wandering about unceasingly for several hours, they 

 "finally fix themselves by the point. All, however, that I have 

 observed, after they had come to rest, became decomposed with- 

 out further organic development, and their contents, which, so 

 long as they were in motion, were always coloured yellow and never 

 blue with iodine, became transformed into a number of very 



