REJUVENESCENCE IN NATURE. 265 



gonidia retain their roundish or rounded polygonal form, 

 but exhibit at one side a hyaline margin, which occupies 

 about a third part, or even half of the circumference; 

 the microgonidia, on the other hand, become distinctly 

 longish, the more acuminated end, at the same time, 

 appearing transparent. The green granules enclosed in 

 the interior are still distinguishable in both, but less 

 sharply, since they begin to blend together; the colour 

 is again bright green, in the net-formers darker, in the 

 swarmers more of a yellowish-green. The ffth stage, 

 that of rest, is connected in the macrogonidia with their 

 union into a young net, which, union begins even in the 

 last period of the movement, so that gonidia, already 

 united in groups, are seen still jerking and pulling back- 

 wards and forwards. When they have come to complete 

 rest, and united perfectly into a new net, the elongation 

 of the previously roundish gonidia begins; the green 

 granules in their interior become completely blended into 

 a homogeneous mass ; the rudiment of the first starch- 

 grain makes its appearance ; the newly formed cell-mem- 

 brane becomes distinguishable. The microgonidia, also, 

 which swarmed-out, and which never unite into nets, but 

 merely become irregularly heaped together, exhibit, after 

 they have come to rest, this transition of the granular 

 contents into a homogeneous green mass, as well as the 

 formation of a small starch-grain and the production of a 

 distinct cell-membrane, by means of which they often 

 become coherent together in groups ; on the other hand 

 they show no trace of elongation, and in general do not 

 increase in size,* while in the young nets the increase of 



* I cannot let this opportunity pass without mentioning one observation, 

 which perhaps somewhat modifies what has been said above. In the vessels 

 of water in which I cultivated Hydrodictyon I frequently found isolated 

 Hydrodicfyon-ce\\s, in groups of four united irregularly together, which 

 became developed, but under these circumstances assumed irregular, bulging, 

 nodulated, or even branched forms. Whether these hermits arose from 

 individual microgonidia, which, as an exception, had arrived at a develop- 

 ment, or from macrogonidia scattered through accidental rupture of the 

 mother-cells in the stage of motion, I could not decide by direct observation, 



