RECENT MEMOIRS ON FRESHWATER RHIZOPODA. 79 



bodies in its constitution are seemingly of move importance 

 in the formation of genera, whilst as regards larger groups 

 the authors are driven back to the characteristics possessed 

 by the pseudopodia as the most comprehensive and promi- 

 nent, and at same time natural and constant, as already long 

 ago laid down by Dujardin and Carpenter : these are the two 

 groups known as Lobosa and Rhizopoda. 



Monothalamia Lobosa. 



The pseudopodia are either cylindrical or finger-like, or 

 form broad plates or lamellse, or they end in a conical 

 manner. They are always blunt at the apex, never very long, 

 rarely and but slightly branch, their protoplasm homogeneous, 

 very rarely any granules passing into them and then only 

 near the base. 



The test is either a pure secretion-product or formed by 

 the cementing together of foreign bodies. 



Arcella vulgaris (Ehrenb.) 



For the first time seemingly a correct description of the 

 structure of the peculiar test of this somewhat variously 

 shaped and otherwise pretty well known, and at least common, 

 species is given by Hertwig and Lesser.^ Two plates, an 

 outer forming the superficies of the test, and an inner applied 

 to the body of the Arcella, are united by a honeycomb-like 

 structure, whose hexagonal cavities form prismatic spaces 

 standing vertically to the surface. These spaces the authors 

 took to be filled with fluid ; in order, however, to test if real 

 hollows or cavities the authors applied a solution of carbonate 

 of soda, adding thereto acetic acid, subsequently washing out 

 with water : the hexagonal spaces then for the most part 

 became filled with air and therefore appeared with the black 

 border indicative of that condition. They therefore conclude 

 that the appearance of the marking on the Arcella test is not 

 due to granulation as Dujardin supposed, nor to perforating 

 canals as held by Ehrenberg, nor built up of individual plates 

 as Claparede and Lachmann, as well as Carter, assumed. 

 Wallich, indeed, spoke of a " symmetrical reticulation" and of 

 " hexagonal interspaces ;" still Hertwig and Lesser doubt if 

 he altogether correctly appreciated the structure, as how other- 

 wise could he come to the surprising conclusion that Arcella 

 vulgaris could be but a subspecies or even species of Difflugia ? 

 A query which I may venture heartily to re-echo. 



' Loc. cit., p. 93 et seq. 



