168 SURVEY OF CELL-LIFE. 



is essentially different from a muscular fibre; while, on the 

 other hand, a whole primitive muscular fasciculus is identical 

 in its mode of origin with a nervous fibre, and so on. The 

 existence of a common principle of development for all the 

 elementary parts of organic bodies lays the foundation of a 

 new section of general anatomy, to which the term philoso- 

 phical might be applied, having for its object — firstly, to 

 prove the general laws by which the elementary parts of 

 organisms are developed; and, secondly, to point out the dif- 

 ferent elementary parts in accordance with the general princi- 

 ple of development, and to compare them with one another. 



SURVEY OF CELL-LIFE. 



The foregoing investigation has conducted us to the princi- 

 ple upon which the elementary parts of organized bodies are 

 developed, by tracing these elementary parts, from their per- 

 fected condition, back to the earlier stages of development. 

 Starting now from the principle of development, Ave will recon- 

 struct the elementary parts as they appear in the matured 

 state, so that we may be enabled to take a comprehensive view 

 of the laws which regulate the formation of the elementary 

 particles. We have, therefore, to consider — 1, the cytoblas- 

 tema; 2, the laws by which new cells are generated in the 

 cytoblastema ; 3, the formative process of the cells themselves ; 

 4, the very various modes in which cells are developed into the 

 elementary parts of organisms. 



Cytoblastema. — The cytoblastema, or the amorphous sub- 

 stance in which new cells are to be formed, is found either 

 contained within cells already existing, or else between them in 

 the form of intercellular substance. The cvtoblastema, which 

 lies on the outside of existing cells, is the only form of 

 which we have to treat at present, as the cell-contents form 

 matter for subsequent consideration. Its quantity varies ex- 

 ceedingly, sometimes there is so little that it cannot be recog- 

 nized with certainty between the fully-developed cells, and can 

 only be observed between those most recently formed; for 

 instance, in the second class of tissues ; at other times there is 



