160 CAPILLARY VESSELS. 
nexion with the central portions of the nervous system by 
means of a single uninterrupted cell. The different parts of 
the body, however, are connected together by another kind 
of uninterrupted secondary cell, namely, the capillaries. The 
capillary system, generated from several primary cells, forms 
one single secondary cell. The cavity of the secondary cell 
communicates with that of the large vessels. Researches are 
still required to decide the question whether these latter are 
mere dilatations of the capillaries, or whether they are formed 
simply by the junction of other elementary parts. In the 
latter case the capillary vessels would open into a cavity alto- 
gether distinct from their own, just as a vegetable cell opens 
into an intercellular space. It sometimes occurs that the cavi- 
ties of certain vegetable cells open directly outwards, but such 
instances are very rare. 
As a primitive muscular fasciculus, a nervous fibre and a 
capillary vessel are corresponding formations in this class; we 
may also compare these structures with the elementary parts 
of other tissues. The elementary cells of all tissues correspond 
with one another, being formed universally according to similar 
laws. A blood-corpuscle, an epithelial cell, a cartilage-cell, an 
elementary cell of areolar tissue (therefore, also a fasciculus of 
areolar tissue formed from it), correspond to an elementary 
cell of muscle, &c. There is no structure analogous to an 
entire primitive fasciculus of muscle or a secondary muscle-cell 
or a nervous fibre amongst the principal component parts of 
the tissues previously discussed, because with them the forma- 
tion of secondary cells only occurs as an exception. A mus- 
cular fasciculus differs, therefore, from a fasciculus of areolar 
tissue, and a primitive fibre of areolar tissue has no analogy 
with a primitive muscular fibre. 
. Si et +t 5 
