34^ 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 progTess 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-units, 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 foui* grades 

 or species of plastids, namely: 1. Sionple cytods (p. 186. 

 Fig. 1 A) ; 2. Encased cytods; 3. Simple cells (p. 188; 



