SECT. 217.] 



LYMPHATIC VESSELS. 



50I 



layer, which may be regarded as a kind of connective tissue ; and 

 while the nuclei of the capillary vessels move closer together, this 

 layer gradually coalesces with the membranous tube. In vessels of 

 o - Oi'", the internal nuclei are already so numerous, as to present 

 unmistakeably the characters of the epithelium; and the outer 

 layer has by this time become increased by a nuclear lamina, the 

 tunica adventitia, so that the vessel is now distinctly lamellated 

 (fig. 198), and we may properly give it the name of a vein. The 

 capillaries, accordingly, appear to become transformed into the 

 larger vessels by the superaddition of layers, both on their inner 

 and outer sides ; their own coat, meanwhile, coalescing with these, 

 and being, perhaps, continued into the fibrous layer of the tunica 

 intima. 



III. — Of the Lymphatic Vessels. 



§ 217. The lymphatics, with the exception of their contents, 

 agree so nearly with the veins, that a short exposition of their 

 structure will suffice. 



Fig. 205. 



Capillary lymphatic vessels, from the tail of a tadpole ; magnified 350 times, a. 

 Membrane of the same; 6. processes which they form; c. remains of the contents of 

 the cells which form these vessels, in which nuclei lie concealed ; e. caecal terminations 

 of the vessels ; /. such a one still pretty distinctly recognisable as a formative cell ; g. 

 isolated formative cell in the act of uniting with the real vessels. 



