460 Dr. G. C. Wallich on the Distinctive Characters, Habits, 



allude to the enclosure of one or more of these Diatoms within 

 a distinct capsule, which it has been customary to regard as indi- 

 cative of encystation, connected either with the production of its 

 sporangium or with some heretofore unrecognized reproductive 

 process. 



The frustules, when simply surrounded by this capsule, and 

 nearly altogether deprived of their soft and coloured contents, 

 could hardly convey any other impression than that they are 

 undergoing one or other of these processes; for there are no 

 characters discei'nible in the capsular investitui'e whereby its real 

 source and function could be determined. And, coupling the 

 undoubted faculty possessed by the Diatomacese, of occasionally 

 secreting in augmented quantity the gelatinous film by which 

 they are normally surrounded at all times, with the occasional 

 imprisonment of more than one frustule, it is only necessary to 

 assume that the external layer of this film becomes consolidated, 

 and the appearances would seem to be sufficiently accounted 

 for. But wherever the distinct capsular investiture is present, 

 for reasons now about to be adduced, such an explanation would 

 appear to be erroneous, and the condition described to be de- 

 pendent on animal, and not on vegetable, agency. In short, an 

 Amoeba has become encysted, and not a Diatom*. 



In the course of some experiments on feeding freshwater 

 Rhizopods by artificial means, towards the close of last month 

 (October) my attention was particularly drawn to this subject 

 on perceiving that in some of the Hampstead material then 

 freshly procured, but nevertheless presenting traces of disin- 

 tegrative decay, a large proportion of the Amoeba were distended 

 (as in the case of some of the specimens referred to in my paper 

 of April last) with frustules oi Pinnularia, and that, whilst these 

 Amoeba were rapidly ridding themselves of the rest of their ex- 

 traneous contents, they appeared to select and retain those frus- 

 tules which were most copiously charged with endochrome and 

 oil-globules, and to be gradually assuming a consolidated invest- 

 ing layer. 



The artificial food employed consisted of weak solutions of 

 gum and gelatine. Deeming it possible, however, that the 

 intermixture of these substances with the water containing the 

 Amoeba might have something to do with the encysting process 



* In speaking of the solitary example of an encysted Amveba recognized 

 by me at the time my observations contained in the ' Annals ' for May 

 (p. 368) were written, I was unaware that Schneider had pointed out the 

 occurrence of a " resting-stage " in the history of Amoeba. This writer 

 distinctly refers to the formation of a membranous sac, although he failed 

 to trace the encysting process beyond this point. My observations on this 

 head, in the last Number of the ' Annals ' (p. 334), ought, therefore, to be 

 regarded as su))pleraentary to and confirmatory of his. 



