346 THE HISTORY OF CREATION. 
of an external crust, which as a protecting covering shut in 
the softer interior from the hostile influences of the 
outer world. As soon as, by condensation of the homo- 
geneous Moneron, a cell-kernel arose in the interior and 
a membrane arose on the surface, all the fundamental 
parts of the unit were furnished, out of which, by infinitely 
manifold repetition and combination, as attested by actual 
observation, the body of higher organisms is constructed. 
As has already been mentioned, our whole understanding 
of an organism rests upon the cell theory established thirty 
years ago by Schleiden and Schwann. According to it, 
every organism is either a simple cell or a cell-community, 
a republic of closely connected cells. All the forms and 
vital phenomena of every organism are the collective result 
of the forms and vital phenomena of all the single cells of 
which it is composed. By the recent progress of the cell 
theory it has become necessary to give the elementary 
organisms, that is, the “ organic” individuals of the first 
order, which are usually designated as cells, the more 
general and more suitable name of form-uwnits, or plastids, 
Among these form-units we distinguish two main groups, 
namely, the cytods and the genuine cells. The cytods are, 
like the Monera, pieces of plasma without a kernel 
(p. 186, Fig. 1). Cells, on the other hand, are pieces of plasma 
containing a kernel or nucleus (p. 188, Fig. 2). Each of 
these two main groups of plastids is again divided into two 
subordinate groups, according as they possess or do not 
possess an external covering (skin, shell, or membrane). 
We may accordingly distinguish the following four grades 
or species of plastids, namely: 1. Simple cytods (p. 186, 
Fig. 1 A); 2. Encased cytods; 3. Simple cells (p. 188, 
