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



It is in the configuration of the test, however, that the most 

 striking peculiarity occurs. In figure it is like that of the pyri- 

 form variety of D. proteiformis ; but, instead of being built up 

 of irregular mineral particles, so as to present a rugged outline 

 exteriorly, it was entirely composed of hyaline rectangular plates, 

 arranged with the greatest regularity in consecutive transverse 

 and longitudinal series — the smaller plates being disposed at the 

 two extremities, whilst the larger ones occupied the central and 

 widest portion of the structure. This specimen is represented, 

 in its mounted state, in the plate appended to this paper (fig. 16), 

 under the name of D. proteiformis, var. symmetrica. 



Of the chemical composition of these remarkable rectangular 

 plates I am as yet unable to give any definite account. But 

 there is some reason to believe they are crystalline and siliceous 

 in their nature, — in the first place, from the perfectness of the 

 angles and their resisting the effects of the heat to which the 

 specimen was subjected during mounting in balsam ; and in the 

 second, from their exhibiting no coloration when seen with the 

 aid of the polariscope. 



The second aberrant form, however, involves not the test, but 

 the animal inhabiting it, at least so far as the preponderance of 

 evidence goes, and is in fact but an example of the transition, 

 in a testaceous Rhizopod (namely, Diffiugia proteiformis, var. 

 acuminata), of the typically lobose pseudopodia into those of an 

 Euglypha or Gromia*. 



In the specimen under notice, the large and coarse sandy 

 particles entering into the formation of the test completely pre- 

 cluded observation of the characters of the soft parts within. 

 But it is almost unnecessary to point out that, whatever these 

 may have been, if betokening a Gromia, the test must be re- 

 garded as abnormal ; if a Difflugia, the pseudopodia must be so. 



It is well known that the Amcebee are generally to be found in 

 shallow pools or streamlets, more or less charged with disinte- 

 grating organic matter, and liable to stagnate, or to become 

 altogether dried up, by periodical failure of the water-supply. I 

 say, charged more or less with organic matter undergoing disin- 

 tegration, because it is an error to suppose that the Amoeba, or 

 indeed any of the Bhizopods, are able to continue existence long 

 in water which has parted with its oxygen to the extent of be- 



* I may repeat in this place the statement made in a former com- 

 munication (Annals, August, p. 123), that I had detected a distinct 

 nucleus in Gromia oviformis, and at a later period, but only once, an 

 equally distinct contractile vesicle. But, until further opportunities pre- 

 sent themselves of determining whether or not these organs occur uni- 

 versally amongst all the members of the genus, I would reserve my final 

 opinion on the subject. 



