1082 The American Naturalist. [December, 
covered with denticulations of uniform size, as they are seen on 
broken shells of Cyphoderia, each tooth representing a siliceous. 
disc. I ascertained also that these shells resist very well a red 
heat, but after the action of boiling sulphuric acid I was not able 
to find the discs with certainty. 
As for the origin of all these regular siliceous elements in 
Rhizopods, it is well known now that it must be looked for in the 
plasma itself. The animal has the power of secreting these sili- 
ceous plates in the very inside of its body, and in many species 
(Quadrula, Euglypha, etc., etc.) these plates can be seen very 
frequently in the plasma, either lying there without any order, 
or, on the contrary, disposed in regular layers. I will mention 
here that the species Cyphoderia has always been described as 
very generally containing, especially at the posterior part of its 
- plasma, a considerable number of shining, very refractive grains, 
that were supposed to be starch or excretion granules. Now I 
have been able to isolate these granules, and to satisfy myself that 
they resist both red heat and boiling sulphuric acid,—a fact which 
proves them to be siliceous, and to represent nothing but plates 
in course of formation, destined ultimately to build up another 
shell. It is well known, indeed, that these reserve plates (Reserve- 
plattchen), as they have been called, will not be of any use to the 
animal that formed them, but serve to make up a shell for a new 
animal. An individual A, for instance, full of reserve plates, 
expels these plates through its mouth, together with some of its 
own plasma. The whole plasma becomes highly vacuolated, and 
thus augments in volume; the expelled portion, still attached to 
the mouth of the parent, takes the form of the species, and the 
plates are disposed as an outer covering, and in the most beautiful 
order. ; 
These reserve plates are certainly a product of the animal itself, 
which has thus the power of secreting silica. Besides, from very 
numerous observations on shells (especially Nebela) on which all 
transitions are to be seen from perfect diatom cases to very simple 
rods that have lost all precise form, it appears certain to me that, 
as Wallace suggested, the plasma of Rhizopods has the power of 
home and partly dissolving the shells of diatoms. 


