VILLI. 



[ 676 ] 



VILLI. 



but the relations are still somewhat obscure, 

 and this is even more the ease with Spirillum 

 and the rest, which are excluded there. We 

 think it advisable, therefore, to add here a 

 table of the genera according to the views of 

 those who regard them as Infusoria, or at 

 all events as a distinct family. More details 

 are given under the respective heads. 



Filament r Inflexible 1 . Bacterium. 



straight. I Flexible like a serpent 2. Vibrio. 



Filament/ ^P^^^ ^^^^^^^ ^' fP"!^"^"' . . 



P^^ * t Spiral flat, like a watch-spring 4. S/?»'ocZjscms. 



They are best preserved by allowing them 

 to drj' spontaneously on the slide. 



For Vibrio tritici see Anguillula tri- 

 tici. 



BiBL. Ehr. Infus. p. 73 ; Dujardin, Infus. 

 p. 209. 



VILLI. — These are minute folds or pro- 

 longations of the mucous membrane of the 

 small intestines. They are most numerous 

 in the jejunum and ilium; in the former 

 conical and flattened, sometimes plate-like. 



Fig. 806. 



cylindrical, club-shaped or filiform; whilst 

 in the latter they are broader and flattened. 



The villi form solid processes of the 

 mucous membrane, consisting of areolar 

 tissue without elastic elements, but abound- 

 ing in roundish nuclei ; containing also 

 blood-vessels, lacteals and unstriated mus- 

 cular fibres. 



Their sm*face is covered with a basement 

 membrane, and a single layer of cylindi'ical 

 epithelial cells. 



The villi are exceedingly vascular, and form 

 beautiful microscopic objects when injected ; 

 exhibiting a network of capillaries with 

 rounded or elongate meshes. 



Each villus contains a lacteal, the ongin of 

 which commences either in a single csecal 

 dilatation, or in a network of branches. 



The muscular fibres form a thin layer, not 

 very distinct in man, surrounding the lacteals, 

 and capable of greatly contracting or short- 

 ening the villi. 



The epithelial cells are intimately con- 

 nected with each other, but easily detached 

 from the villi, often in groups or rows. 



Fig. 807. 



MHmk 



Fig. 806. Intestinal villus of a kitten, free from epithelium, and after treatment with acetic acid, a, boundary' of 

 vUlus ; 6, subjacent nuclei ; c, nuclei of the muscular fibres ; rf, roundish nuclei in the middle of the villus. JWagnified 

 350 diameters. 



Fig. 807. A, magnified 75 diameters. Two villi with their epithelium, from a rabbit, a, epithelium ; b, parenchyma. 

 B, magnified 300 diameters. A row of detached epithelial cells, a, membrane separated by water. C, magnified 350 

 diameters. Detached epithelial cells, a with, b without the separated membrane ; c, surface view of some epithelial 



