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 poimt 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 foregomg 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, we 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 cytoblastema, which 
hes 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 
