No: 416.) PROTOZOA. OF ESPECIAL INTEREST. 649 
It is not an easy matter to interpret Nuclearia, for it may be 
regarded as a degenerate heliozoan which has lost its axial 
filaments, or as a primitive form which has never had these 
peculiar axial structures. The interpretation involves the old 
dispute over the most primitive forms of Protozoa. Are we, 
with Klebs, to hold that the flagellates were the most primi- 
tive forms ; or with Lankester, that the rhizopods are to be so 
considered ; or with Bütschli, that the flagellated amoeboid 
forms were the-ancestors of both rhizopods and flagellates? 
The problem, to my mind, has no great importance, for, it is 
quite probable that the Protozoa have not come down without 
change from that unknown period of the primitive animal forms, 
while even in historic times they may have been adapted and 
readapted many times over to changing conditions of environ- 
ment. The fact that the majority of Rhizopoda have flagel- 
lated swarm-spores is not sufficient proof that their ancestors 
were flagellated, while on the other hand the frequent amceboid 
condition of the flagellates is equally valid evidence that the 
thizopod form was the older. Flagella and pseudopodia are 
not far removed from one another, and frequent observations 
have confirmed Dujardin's early view that flagella may become 
pseudopodia and pseudopodia flagella. The transitional forms 
such as Dimorpha, Actinomonas, etc., only strengthen the con- 
nection, and it will be shown, I believe, that many of the pseudo- 
podia of Heliozoa are similar to the flagella of the Mastigo- 
phora. Blochmann has shown, for example, that in Dimorpha 
the pseudopodia have axial filaments, which, as in Actinophrys, 
focus in the nucleus or its vicinity, The flagellum, too, is 
focused at the same point, so that in Blochmann's figure the 
axial filaments and the flagellum appear to be the same in struc- 
ture, Artodiscus, according to Pénard, is a heliozoón which 
dances about the field upon the tips of its ray-like pseudopodia. 
In this case the pseudopodia are like so many flagella, for there 
can be no doubt that the motion is due to the contraction and 
elasticity of the pseudopodia and probably of the axial filaments 
in them, Acanthocystis, also, has a slow, rolling motion, by 
means of which it covers a distance equal to twelve times its 
Own diameter in one minute (Pénard). Here, also, although 
