288 THE BLOODVESSELS, BY C. J. EBERTH. 



simplest examples, a fusiform spiral cell presents itself, the 

 lateral surfaces of which are in contact, whilst the extremities 

 occupy the spaces between the ends of adjoining cells. The 

 capillaries in the pecten of the bird, even when extremely 

 delicate, possess small polygonal cells, the breadth and length 

 of which are nearly equal. It is only occasionally, and in the 

 larger vessels especially, that the cells are distinctly fusiform. 



As concerns the substance of which the cells are composed, 

 it is always more abundantly and distinctly granular towards 

 the centre and around the nucleus, whilst near the margin it is 

 quite clear, and thins off to a delicate border. The capillary 

 cells of the pecten of the bird, on the other hand, are, even in 

 profile, only indistinctly fusiform, are of nearly equal thickness 

 at the centre and at the margins, and consist of finely granu- 

 lar protoplasm, with a simple or divided nucleus, the contents 

 of which frequently separate from the investing membrane of 

 the nucleus, in the form of a roundish spherule, resembling a 

 large nucleolus. 



Only a few vascular regions form an exception to these 

 statements ; namely, the capillaries of the liver of Mammals and 

 Amphibia, the chorio-capillaries of the former class, the hyaloid 

 of frogs, and the young capillaries of the tadpole, and of patho- 

 logical products of recent formation. 



After repeated observations, I have only been able to 

 discover the presence of cells in the capillaries in these in- 

 stances, in a few isolated points ; but in their stead I found 

 fusiform or branched nucleated areas on the walls, bounded by 

 finely punctated or interrupted lines. In the chorio-capillaris 

 and the hyaloid membrane of the frog I found fusiform or 

 polygonal cells in some only of the coarser capillaries, whilst 

 in others no trace of them was discernible. 



As regards the significance of these facts, three possibilities 

 exist, either the capillary wall does not consist of cells at all, 

 or, if this be the case, they have disappeared in consequence 

 of fusion with one another, or the capillary wall has become 

 only imperfectly differentiated into cells. 



Now if, after repeated examination, a cellular structure is 

 only demonstrable in the stronger and older capillaries, and 

 but rarely in the younger, the conclusion is admissible, that 



