CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 447 



modified by reason of their position. They are not hidden in the 

 recesses of an alveolus like salivary mucous cells, (hey do not form 

 a layer by themselves like the gastric mucous cells, but are scat- 

 tered among other cells carrying on important functions. Hence 

 apparently their shape of a goblet and their well-defined mouth. 

 A goblet cell to start with is a cell of a more or less columnar 

 form and ordinary protoplasmic cell-substance. The cell-substance 

 manufactures and becomes studded with granules or spherules 

 which very speedily give rise to mucin, the cell swollen with its 

 load assumes a goblet shape, and the formation of a mouth in the 

 space between the converging refractive borders of neighbouring 

 columnar cells assists in the discharge of the load. 



The columnar cells of the villus are, as we shall see, chiefly 

 occupied in the reception of material from the intestine into the 

 body of the villus ; the goblet cells are chiefly occupied in secreting 

 into the interior of the intestine mucin and possibly some of the 

 constituents of the succus entericus. 



Below this layer of columnar and goblet cells extends the thin 

 basement membrane, above which, between the bases of the other 

 cells, may be seen small cells, that is to say, cells with a relatively 

 small quantity of cell-substance round the nucleus ; these have 

 been taken to be reserve or replacement cells. But at times 

 clearly recognizable leucocytes may be seen between the columnar 

 cells ; these have probably wandered into the epithelium from the 

 body of the villus ; and it may be that some of the small cells in 

 question are of an allied nature. 



262. The centre or rather the axis of the body of the villus 

 is occupied by a club-shaped space, sometimes bifurcate or even 

 branched at. the distal end, varying indeed a great deal in different 

 animalsr^This is the central lymphatic space or ' lacteal radicle,' 

 as it has been called, which may be filled with fatty or other 

 material, or, as more frequently is seen in hardened preparations, 

 may be empty and collapsed. It is lined with epithelioid plates, 

 and is at the base of the villus continuous with the lymphatic 

 passages and vessels of the mucous membrane. It will be con- 

 venient to defer the further study of this lymphatic space until 

 we come to deal with the lymphatics generally. 



Between this lymph-space, and the basement membrane, 

 generally close underneath the latter, lies a fairly close-set net- 

 work of capillary vessels, especially well developed towards the 

 upper part of the villus. This network is fed by generally one 

 small artery which springing from the arteries of the submucous 

 tissue splits up into capillaries towards the middle of the villus ; 

 and the blood of the capillaries passes into veins, generally two, 

 which in a similar manner pass down to the veins of the submucous 

 tissue. 



Between the basement membrane and the central lymph-space, 

 are also found a number of plain muscular fibres, some running 



