g2 Animal Morphology. 



of contraction of a very abiding character did not exist in 

 this structure, how it could remain in a contracted condition, 

 and narrowing the calibre of an artery for long, and at 

 another time leaving it dilated according to the amount of 

 fluid passing through it, if the true beaded muscle had all 

 the work to do, and in its action it was not supported by a 

 slower and more abiding form of contraction. 



The membrane just described gives an excellent illustra- 

 tion of the adaptation of tripartite membranes to other 

 membranes of very widely different cell differentiation, since 

 the capillaries reach almost every tissue of the body. 



Added to the circulatory system is the Lacteo-lymphatic 

 system, which is an economic and supplying system to the 

 circulatory. Its structure is in many points similar to the 

 former in its tubing, and ramifies almost every structure of 

 the body. 



Its internal coat is serous, its outer fibrous, and its middle 

 is muscular, but sparingly developed. 



Beyond its being a conductor of aliment through the 

 thoracic duct to the circulatory system, by an entrance into 

 the left subclavian vein near to its junction with the internal 

 jugular, aided by the ductus lymphaticus dexter on the right 

 side, it scarcely appears to perform any duty beyond that 

 of imbibition of prepared aliment from the small bowels, 

 and waste exudations from the capillaries of the system, or 

 effete matter which is not returned into the general cir- 

 culation, and which can be employed a second time to 

 repair destructive processes. 



But in the midst of this conveyance a glandular system, 

 as mesenteric and lymphatic glands, intercepts the course of 

 conveyance, and apparently subjects the chyle, or lymph, to 

 some independent vito-chemical change, and may be adds, 

 through a process of cell destruction, fresh material in such 

 way and measure as produces in the moving fluid a gradual 



