Animal Morphology. 91 



serous membrane, with an external fibrous structure, which 

 fibrous membrane appears to be the basement of the mucous 

 membrane, and has suffered an apparent arrest of all further 

 mucous structure till it arrives at the capillary system, to 

 which it has been transposed. Here the peculiar active cell- 

 appropriating and eliminating powers (which are supplemented 

 by supplying capillary vessels to the muco-glandular structures 

 in the great alimentary mucous membrane) indicate a close 

 approximation in the capillary system to the function of mucous 

 membrane, where much destructive cell change is ever going 

 on, with an occasional economic ulterior end, as in the 

 pancreatic and biliary secretions. 



But in the capillary system the serous structure almost, 

 if not entirely, disappears, and the capillary tubing is little 

 else than enclosed walling, where active cell destruction is 

 going on, and is abetted by exosmose and endosmose, 

 aiding in the process of appropriating new and eliminating 

 old material, between the moving blood current and the 

 greater or less stationary structures through which it 

 passes. 



This, then, gives us a sample of partial membranous 

 displacement in the capillary system, where the membrane, 

 in its basement part, is running along in the veins and 

 arteries, with its complimentary serous membrane, through 

 most of its course, and the active functional tubing is 

 placed half between the arteries and veins, under the title of 

 the capillary system. 



The muscular membrane in the circulatory system, both 

 in arteries and veins, occupies the middle coat, but is 

 sparingly distributed to them, unless it be at some particular 

 point here and there ; but the middle elastic fibrous coat of 

 the larger arteries is probably composed, in a great measure, 

 of differentiated contractile membrane in a low meta- 

 morphic form ; for it is difficult to conceive, if some low form 



