16 BRITISH FRESHWATER RHIZOPODA. 
Ameba rolls up a filament of conferva.* Egg-albumen 
and gum-arabic in solution evinced the same pheno- 
mena, the rapidity of ingestion showing the density of 
the medium. These phenomena accord with physical 
laws. Rhumbler found that a splinter of glass inserted 
in a drop of chloroform suspended in water will leave 
the chloroform and seek the water, but that, coated with 
shellac, and then placed in contact with the chloroform 
drop, the splinter and shellac were quickly drawn into 
the chloroform. So soon as the shellac was dissolved by 
this medium, it was expelled, or, to put it more cor- 
rectly, drawn into the surrounding water, by reason of 
the greater co-efficient of adhesion between glass and 
water. Rhumbler drew an analogy between this and 
the process of feeding in the Rhizopoda. Bodies, he 
concluded, are ingested into the plasma because of the 
greater attraction to the fluid protoplasm than to the 
water; then, through the chemical changes between 
protoplasm and the digestible parts of the foreign sub- 
stances, the constituents of. the body are changed, and 
a corresponding change is wrought in the attractive 
force which keeps them together, that is, in the co- 
efficient of adhesion, and defecation results. 
Tue Tests. 
The tests of the freshwater Rhizopoda are variable 
in size and form, as well as in the materials of which 
they are composed. The simple membranous test of 
the Cochliopodia, or that of Pamphagus hyalinus, may 
be regarded as the most rudimentary. It is formed 
by the secretion of a chitinoid substance, apparently 
during the life of the individual. From this, as a 
starting point, we get a great diversity of structural 
types, from the homogeneous tests of the Hyalosphenix 
to the tesselated ones of Nebela and Euglypha, and the 
coarser Difiiigie, which, not content with a purely 
« An Amaba 90 p in length absorbed and coiled up an Oscillaria filament 
measuring 540 p. 
