ELASTIC TISSUE. 129 



The formation of the fibres of areolar tissue from cells, having 

 been typified already in the second class, it follows that orga- 

 nization, or the presence of blood-vessels, does not establish 

 any essential difference in the growth of the elementary par- 

 ticles ; for this class belongs to the perfectly organized tissues, 

 and areolar tissue is highly vascular. The unorganized tissues 

 were formerly said to grow by apposition, and the organized 

 by intussusception. We have already discussed this distinction 

 at page 95. It is so far correct, that the young cells of unorga- 

 nized tissues are not formed throughout the entire thickness of 

 the tissue, but only in the neighbourhood of that surface, on 

 which they are in contact with vascular substance, and where 

 they therefore obtain the freshest cytoblastema. But if this 

 distinction between the surface and parenchyma of the tissue 

 be not present, in consequence of the blood-vessels being dis- 

 tributed throughout its whole thickness, the young cells are 

 then also generated in every part of the tissue ; and such is 

 the case with areolar tissue. The primary distinction, there- 

 fore, merely consists in the absence or presence of vessels, the 

 difference in the place of formation of the new cells being but 

 a secondary distinction. The elementary particles grow in both 

 instances and by the same powers. We shall see hereafter how 

 far the presence of vessels facilitates certain processes which 

 occur during growth. The essential phenomena of growth, 

 and, therefore, also the fundamental powers called into activity 

 by it, are similar in both. But why a formation of vessels 

 should take place in areolar tissue and not in epithelium, is a 

 question for future discussion. 



class v. 



Tissues, generated from cells, the tvalls and cavities of which 



coalesce together. 



The following is the type of formation in this class : inde- 

 pendent cells, by which we mean such as have a special wall and 

 cavity, are present in the first instance ; these we shall call 

 primary cells. They are either round or cylindrical, or of a 

 stellate figure. When round or cylindrical, the primary 

 cells are applied together in rows, the contiguous portions of 



