PROTOCOCCUS PLUVIALIS. 531 



plants, does not occur. The central coloured globule, 

 lying in the colourless envelope, is certainly sharply 

 defined, but not as in the still cells, surrounded with a 

 strong double contour line, but with a delicate simple one, 

 which gives it a peculiar soft appearance. Either by me- 

 chanical means, or by chemical reagents, the internal 

 globular mass may suddenly be made to lose its contour, 

 and to spread so as entirely to fill the cavity of the colour- 

 less envelope. From which it would appear that the 

 internal globular body is not surrounded by any special 

 cellulose-membrane, but only by one readily destroyed 

 by chemical or physical agency, probably nothing more 

 than a dense layer of protoplasm. Whilst, on the other 

 hand, the external membrane represents a true cell- 

 membrane, enclosing between itself and the coloured 

 substance a colourless, aqueous fluid, probably pure or 

 nearly pure water. 



The motile form of Protococcus, therefore, consists, as 

 it were, of two cells, one within the other, both of which, 

 however, differ essentially from the common vegetable 

 cell: the external having a true cell-membrane and 

 aqueous contents; the other, or internal one, with 

 denser, muco-gelatinous, coloured contents, but without 

 a true, rigid (starre) cell wall. Cohn proposes to call the 

 external transparent vesicle the " enveloping cell" (hiill- 

 zelle), and the internal coloured one, the "primordial 

 cell." The term "primordial sac, or utricle," which 

 nearest corresponds to this organism, can only be applied 

 to its peripheral layer, and not to that together with the 

 contents; and the term "amylid-cell" of Kiitzing in- 

 volves a chemical error. 



Neither of these bodies are true, perfect cells, inasmuch 

 as the former wants the primordial utricle, and the second 

 is without the true cell-membrane. The two together 

 would represent the perfect cell; and the entire aspect 

 corresponds, externally perhaps, to a plant-cell in which 

 the primordial utricle has become detached from the cell- 

 membrane and contracted itself into a globular mass in 



