16 BRITISH FRESHWATER RHIZOPODA. 



Amwba 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. 



THE 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 Pamphagiis liyalinus, may 

 be regarded as the most rudimentary. It is formed 

 by the secretion of a chitinoid substance, apparentlv 

 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 Hyalosplieniw 

 to the tesselated ones of Nebela and Euglypha, and the 

 coarser Difflugix, which, not content with a purely 



* An Amoeba 90 /i in length absorbed and coiled up an Oscillaria filament 

 measuring 540 n. 



