REJUVENESCENCE IN NATURE. 229 



sess no cellulose layers at all, such as we have undoubtedly 

 observed in the transitory generations of cells, through 

 which is effected the formation of the gonidia of many 

 Algae, {Ulothrix, Characium, Pediastrum, Cystococcus, 

 Chlamidococcus, &c.) 



Having made these preliminary observations, I shall 

 endeavour to bring together, in a connected summary, 

 the various kinds of reconstruction of the cell, beginning 

 with the cases of entire metamorphosis of the contents. 



A. Reconstruction without division of the cell. 

 —Here the character of the rejuvenised cell either remains 

 essentially the same, i. e., the repeated reconstruction ap- 

 pears merely as a development of the cell advancing by 

 periodical Rejuvenescence, as is the case more or less 

 evidently in the completing development of all vegetative 

 cells; or the character of the rejuvenised cell becomes 

 different, the previously vegetative cell acquiring a 

 reproductive destination, at the same time being freed, 

 in its renewed structure, from the envelope previously 

 formed. In the latter case the rejuvenised cell will be 

 regarded as a new one, notwithstanding t*hat, if we leave 

 out the inessential membrane which it throws off, it is 

 still the old, in reference to its essential part, the internal 

 body, as much as it is in the former case, only its shape 

 being changed. The intermediate stages to be enumerated 

 will show that these two cases are not so different as they 

 seem at first sight. We accordingly distinguish — 



1. Reconstruction without division in vegetative cells, 

 prepared by the periodical nocturnal respiration; ex- 

 pressed in the lamellar deposition of the cell-membrane 

 (p. 220). 



a. The layers of cell-membrane are intimately adherent 

 together, and form a firmly-united, compound cell- 

 membrane, the layers of which are sometimes clearly 

 evident, but often only to be made out by artificial 

 loosening by means of chemical reagents, e. ff. Hydro- 

 dictyon, Cladophora* 



* See- H. V. Mohl, ' Vermischte Schriften,' t. xiii, f. 13, 14. 



