REJUVENESCENCE IN NATURE. 169 



appears to be still devoid of a coat. Only transitory cell- 

 formations, as I have endeavoured to show in certain 

 examples above, remain without a coat of cell-membrane, 

 and in the active gonidia of the Algae (with the exception 

 of the permanently moving cells of the Volvocinese), the 

 commencement of the formation of the cell-membrane, in 

 all probability, does not commence until after the stage 

 of ciliary motion, the endurance of which is, however, 

 mostly very short, never extending beyond a few hours. 



We have already ascribed, in the foregoing, thft 

 accurate limitation of the cells not yet clothed with a 

 cell-membrane, to a coat belonging to the very body of 

 the cell, not to be confounded with the cellulose envelopes; 

 and we have sought especially to characterise as an 

 example of this, the ciliated coat of the gonidium of 

 Vaucheria, which may fully claim the title proposed by 

 Mohl — "primordial utricle." Whether, however, the 

 occurrence of such a coat, distinguishable from the 

 remaining mucilaginous contents or protoplasm of the 

 cell, as we see it in Vaucheria, is an universal pheno- 

 menon, or whether the primordial utricle described by 

 Mohl* is not rather a mere coat of protoplasm, a layer of 

 mucilage lining the inside of the cell-wall, f produced 

 through the protoplasm, originally wholly filling the cell, 

 becoming excavated by a cavity filled with watery fluid, 

 is a question which requires for its settlement more exact 

 and extensive researches than we at present possess. 

 Isolated, easily observed cases do indeed indicate that 

 the mucilaginous layer of full-grown cells is not a simple 

 protoplasmic investment, but is composed of two or three 

 differently organised layers, the outermost of which, re- 

 presenting the proper coat of the cell-contents, is very 

 probably formed in the earliest period, as the original 



* Vide H. von Mohl, ' Bemerk iib. den Bau des veg. Zelle.,' Bot. Zeit., 

 184.4, p. 275. ('Trans. Taylor's Seient. Memoirs,' vol. iv, pp. 91-92) ; and 

 ' Ueb, die Saftbew im Innern der Zellen,' 'Bot. Zeit.,' 1846, p. 74. ('Transl. 

 Annals of Nat. Hist.,' vol. xviii, p. ], 1845.) 



t This ia Nageli's view, (' Zeitbchr.,' 1844, p. 91,-1847, p. 38). 

 Transl. in Ray Society's publications, 1845, p. 268, — 1849, p. 110. 



