74 THE CELL DOCTRINE. 



with the animal primordial substance or sarcode. 

 Schultze illustrates his definition by the embryo cells 

 resulting from the segmentation of the ovum, as 

 typical cells, which are thus composed of protoplasm 

 surrounding a nucleus, which nucleus, as well as pro- 

 toplasm, are products of like constituent parts of 

 another similar cell. "The cell leads in itself an 

 independent life of which the protoplasm is espe- 

 cially the seat, although to the nucleus also undoubt- 

 edly falls a most important, though not yet precisely 

 determined role. Protoplasm is for the most part no 

 further distinct than that it will not commingle with 

 the surrounding medium, and in the peculiarity that 

 with the nucleus it forms a unit. Upon the surface 

 of the protoplasm, there may form a membrane, 

 which, although derived from it, may be chemically differ- 

 ent, and the assertion that it is the beginning of a retro- 

 gression may be defended. A cell with a membrane can 

 not divide itself, unless the protoplasm within the 

 membrane divides itself. A cell within a membrane 

 chemically different from protoplasm, is like an en- 

 cysted infusorium."* 



Briickef went even further in his definition, and 

 said that it was not shown that the nucleus even is 

 an essential element of the cell. In proof of which 

 he adduces the cells of cryptogams. Facts in justi- 

 fication of Briicke's doubt are adduced by StrickerJ 

 in the discovery by Max Schultze, in the Adriatic 



* Schultze, Max, Protopl. d. Khizopoden. Leipzig: 1863. 

 f Briicke, E., Die Elementarorganismen, p. 18-22. 1861. 

 J Strieker, op. citat, p. 6. 

 $ Schultze, Max, Organis. d. Polythalam. 1854. 



