504 



ANATOMY OF VEliTEBRATES. 



CHAPTER XXXI. 



390 



ABSORBENT SYSTEM OF MAMMALIA. 



341. Lacteals.- -In Mammalia the intestinal villi constitute a 

 modification of surface intimately related to the formation and 

 more especially to the absorption, of chyle. Such villi, e. g. of a 

 calf killed after being fed with milk, exhibit, when magnified 



as in fig. 390, a central canal, dilat- 

 ing towards its end, c, white or opaque 

 with chyle : it appears to be an ex- 

 cavation in the substance of the 

 villus, and the only definite tunic is 

 the limitary membrane, a ; from which 

 the epithelium (shown in fig. 350, o) 

 has been removed. The columnar 

 cells of which this epithelium is com- 

 posed are the direct agents of absorp- 

 tion. Each cell becomes gradually 

 filled by a clear globule of refrac- 

 tive fluid, like oil. The scattered 

 cells which are first filled, cause 

 parts of the surface of the villus 

 to glisten, as in fig. 391, in contrast 

 with the darker tracts of unfilled 

 cells. The oil-like globule next un- 

 dergoes changes, represented in the 

 cell-series, fig. 392, which mainly 

 consist in a subdivision or reduction 

 of the globule, d, to the granular 

 state in a, the nucleus of the colum- 

 nar cell remaining unchanged. These 

 granules, or molecules, escape by 

 rupture or solution of the cell-wall, penetrate the limitary 

 membrane, become aggregated in the basal tissue of the villus, 

 and finally enter the lacteal canal. Dead animal membrane does 



Intestinal villi with lacteal canal, Calf, 

 magn. CLXXVIII". 



