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. 



