650 THE AMERICAN NATURALIST. [Vor. XXXV. 
less than in Artodiscus, the pseudopodia are probably con- 
tractile. 
There thus appears to be some morphological ground in 
favor of the hypothesis that Rhizopoda may have originated 
from the Mastigophora and through the Heliozoa.  Artodiscus 
and Acanthocystis may be regarded as having many flagella of 
modified form, while Dimorpha, which has a typical flagellate 
stage, has one true flagellum and at the same time pseudo- 
podia of the heliozoan type. In Actinophrys, Sphzrastrum, 
Heterophrys, etc., the contractile element, whatever it is, is 
lost, and the pseudopodia appear rigid and apparently serve no 
purpose in movement. They are of the same type, however, 
as in Artodiscus and Dimorpha, and, as in the latter, they 
center at a common point to form a system of rays very much 
like a centrosphere in Metazoa. In Actinosphzerium the rays 
no longer focus in a common center, although each ends in the. 
vicinity of some nucleus. 
In respect of the axial filaments the Foraminifera apparently 
represent an intermediate stage between the Heliozoa and the 
fresh-water Rhizopoda. It has been frequently pointed out that 
the central portion of the pseudopodia of these forms is dense 
and stiff as compared with the outer plasm, which has the typi- 
cal flowing motion of a rhizopod, thus reversing the conditions 
of one of the lobose forms. 
If the relations as outlined above would hold good between 
the Heliozoa and the Mastigophora, then Nuclearia, having lost 
its axial filaments, finds its real position as an intermediate form 
between Heliozoa and fresh-water rhizopods, retaining, however, 
the fine and needle-like pseudopodia of the Heliozoa. Considered 
in this connection it would be a degenerate form, The entire 
argument, however, might work equally well the other way, 
and it might be held that an Amoeba such as A. radiosa, OF 
A. tentaculata, or Nuclearia, develops vibratile pseudopodia hav- 
ing an axial filament of especial contractile substance. The 
foraminiferan pseudopodia would be a first step in such a 
development, Acanthocystis, Artodiscus, and Dimorpha succes- 
sive following steps, until a flagellate would be the outcome. It 
would be difficult only to place Actinophrys, Actinospheerium, 
