FOUR OEDERS OF PLASTIDS. 347 



Fig. 2B)\ 4. Encased cells (p. 188, Fig. 2 A). (Gen. Morpli. 

 I 269-289.) 



Concerning the relation of these four forms of plastids 

 to spontaneous generation, the following is the most 

 probable : — 1. The simple cytocls (Gymnocytoda), naked 

 particles of plasma without kernel, like the still living 

 Monera, are the only plastids which directly come into 

 existence by spontaneous generation, 2. The enclosed cytods 

 (Lepocytoda), particles of plasma without kernel, which are 

 surrounded by a covering (membrane or shell), arose out of 

 the simple cytods either by the condensation of the outer 

 layers of plasma or by the secretion of a covering. 3. The 

 simple cells (Gymnocyta), or naked cells, particles of plasma 

 with kernel, but without covering, arose out of the simple 

 cytods by the condensation of the innermost particles of 

 plasma into a kernel, or nucleus, by differentiation of a 

 central kernel and peripheral cell-substance. 4. The 

 enclosed cells (Lepocyta), or testaceous cells, particles of 

 plasma with kernel and an outer covering (membrane or 

 shell), arose either out of the enclosed cytods by the forma- 

 tion of a kernel, or out of the simple cells by the formation 

 of a membrane. All the other forms of form-units, or 

 plastids, met with, besides these, have only subsequently 

 arisen out of these four fundamental forms by natural 

 selection, by descent with adaptation, by differentiation 

 and transformation. 



By this theory of plastids, by deducing all the different 

 forms of plastids, and hence, also, all organisms composed 

 of them, from the Monera, we obtain a simple and natural 

 connection in the whole series of the development of nature. 

 The origin of the first Monera by spontaneous generation 



