REJUVENESCENCE IN NATURE. 263 



a more or less brownish tinge, sometimes appearing wholly 

 tilled with granules, sometimes displaying a lighter space, 

 free .from granules, in their centres. In correspondence 

 with the shape and the (in the same mother-cell) tolerably 

 equal size of the plates, they are so arranged that mostly 

 six are grouped round a central one. The size of the 

 plates varies according as they are to form macrogonidia 

 (net-formers) or microgonidia (swarmers) ; in the former 

 case the diameter amounts to about jigth millim., in the 

 latter to jjoth or ^gth ; the latter, moreover, exhibit a less 

 regular, more oblique shape, and less numerous (only 

 4—10) chlorophyll granules. The membrane of the 

 parent-cell begins to thicken by swelling-up in this stage. 

 In the third stage, finally, is effected the complete 

 separation of the little plates, and the formation of the 

 gonidia. The plates, already previously clearly defined 

 against the light intermediate streaks, begin to round off 

 at the corners, and to become convex at the surface, 

 previously lying flat against the cell-membrane, so that 

 the tabular form passes, not at once into a globular, but 

 into a lenticular form, which compression may still be 

 observed in a slight degree subsequently, in the stage of 

 motion. During this rounding, the lighter intermediate 

 streaks vanish, the gonidia come into direct contact, 

 triangular intercellular spaces only appearing at each 

 point where three meet. This stage is ordinarily of very 

 short duration, passing at once into ihe fourth, that of 

 the movement of the gonidia, which differs in degree and 

 duration, according to the kind and destination of these. 

 Although the phenomena of the motion of the gonidia of 

 Hydrodictyon have been spoken of already, we cannot 

 pass them over entirely here, since certain points come 

 under consideration in it, which have an influence on our 

 judgment respecting the mode of cell-formation which we 

 are now engaged with. Both in the macrogonidia and 

 microgonidia the movement at first presents a mutual, 

 originally scarcely perceptible crowding and pushing, 

 which, when in full course, is comparable with the move- 



