REJUVENESCENCE IN NATURE. 285 



however, are less essential than those on which the fol- 

 lowing subdivisions are founded : 



1. The conjugating cells unite entirely {with membrane 

 and contents), and, completely coalescing without throwing 

 off a membrane, form a seed-cell {spore). — The spore 

 originates here as the direct result of conjugation, not 

 subsequently through a further transformation of the 

 contents after the conjugation ; the conjugation-cell is 

 itself the seed-cell, and does not produce the latter as a 

 new cell within itself. Here refers Palmoglaea, the 

 remarkable, of its kind unique,* conjugation of which 

 was only represented in its commencement by Kiitzing,f 

 described in its further course by Thwaites, but, since he 

 assumed an absorption of the cell-membrane of the com- 

 bining cells, mistaken by him exactly in its most essential 

 peculiarity, f I have mentioned my own observations on 

 the conjugation of PalmoglcBOr above ;§ the minute 

 description of the process, with remarks on the species in 

 ■which the observations were made, will follow in the 

 description of the plates. 



2. The conjugating cells, leaving behind the outer 

 membrane, unite directly to form a reproductive cell. — 

 The occurrence of this case is not improbable, but has 

 not yet been made out with certainty. 



3. The conjugating-cells combine merely their contents 

 {bounded by the primordial utricles), to form the repro- 

 ductive cell ; the dehiscent cell-membrane is deserted. — 

 The conjugation of many Diatomacese || very probably 

 belongs here. The mode in which, according to the 



* Similar cases occur in the animal kingdom, in the ■ Infusoria. See 

 Kolliker on Aetinophrp Sol, in Siebold and KoUiker's ' Zeitschrift,' 18i9, 

 b. i, p. 207, (Transl. in ' Quarterly Journal of Microscopic Science,' vol. i, 

 p. 98, et seq,) The forms figured as Actinophrys difformis, by Ehrenberg, 

 (' Infusionsthierchen,' t. xxxi, f. 8,) doubtless represent conjugating states 

 of Actinophrys Sol. 



•j- Assuming that his Palmofflaa MenegUnii, ('Tab. Phycol.,' 24, iii,) 

 actually belongs to thisgenus, and not to Cylmd/rocystis. 



X 'Annals of Nat. History,' 1849, 2d series, vol, iii, p. 243, t. viii, f. c, 

 (as Coccochloris Sredissonii.) 



§' See pp. 135, 202, and pi. i, figs. 1—28, pi. ii, figs. 1—14. || See p. 132. 



