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 Volvocineae), 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, the 

 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 goriidium of 

 Vauclieria, 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., 

 1844, p. 275. ('Trans. Taylor's Sclent. Memoirs,' vol. iv, pp. 91-92) ; and 

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

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



f This is Nageli's view, (' Zeitschr.,' 1844, p. 91, 1847, p. 38). 

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



