REJUVENESCENCE IN NATURK. 267 



Perhaps it is the same substance in a state of solution, 

 but still viscous, which retains the active gonidia for some 

 time at the periphery of the cavity of the mother-cell, so 

 that the macrogonidia, in vrhich the stage of rest and 

 mutual attachment begins pretty soon, cannot unite 

 otherwise than in the tubular form given by their mode 

 of origin, into a net-like colony. We sometimes perceive 

 in the interior of newly-formed nets, still enclosed in the 

 membrane of the parent-cell, colourless balls of muci- 

 laginous consistence, without distinct outlines, which are 

 coloured yellow by iodine. In the swarm-like escape of 

 the microgonidia, through the burst dehiscence-sacs of 

 the mother-cell, likewise, we sometimes see the swarm 

 interrupted by a mass of mucilage mixed up with and 

 clogging them. Whether these masses of mucilage are 

 the still undestroyed remains of the above-mentioned 

 secreted connecting substance of the gonidia, I do not 

 venture to decide. Ordinarily, after the complete for- 

 mation of the gonidia, the contents of the mother-cell 

 exhibit, besides the gonidia, nothing but water-clear 

 fluid. 



As a proof that the gonidia of the Water-net do not 

 originate free in the contents of the mucilaginous layer, 

 but separate from one another by mutual demarcation of 

 boundaries, out of an originally continuous mass, I may 

 mention the not unfrequent occurrence of twin-gonidia 

 (even of triple groups) in which, on swarmers, two (or 

 three) ciliated points may be distinguished, which are 

 sometimes side by side, sometimes placed at right angles 

 to each other, or are even on directly opposite sides. It 

 is easy to make certain that such forms are not produced 

 by blending of previously separate gonidia, but that the 

 light line of division, as formed in the second stage, is 

 omitted between the two plates or groups of contents ; 

 that, consequently, the mutual external definition be- 

 tween two (or three) inwardly separated cells, has not, or 

 only imperfectly, been effected. 



The formation of the gonidia of Ascidium (p. 128), 



