152 



STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



the lacteals ; and it is maintained by Prof. Goodsir, who first brought 

 them into notice, that these globules are really cells , and that it is by 



Fig. 31. 



Diagram of mucous membrane of Jejunum, when absorption is not going on; a, epithelium of a villus; b. 

 secreting epithelium of a follicle; c, c, c, primary membrane, with its germinal spots or nuclei, d, d; e, germs 

 of absorbent vesicles; /, vessels and lacteals of villus. 



their, growth and nutrition that the milky fluid, or chyle, is selected from 

 the contents of the digestive cavity. Their function, therefore, would 

 be precisely the converse of that of the secreting cells already described ; 

 whilst the history of their individual lives is the same. These absorbent 

 cells draw their materials from the fluid in the digestive cavity, instead 

 of from the blood ; and when they burst or liquefy, they set free their 

 contents where they may be taken up by a lacteal and conveyed into 

 the circulating current, instead of pouring them into a cavity through 

 which they will be shortly expelled. In the intervals of the digestive 

 process, however, the extremities of the villi are comparatively flaccid ; 

 and instead of cells, they show merely a collection of granular particles 

 (Fig. 81, e)j which are considered by Prof. Goodsir to be cell-germs. 

 There is considerable doubt, however, whether these supposed cells are 

 anything else than oil-globules ; and whether the real agents in the 

 selection of chyle are not the epithelium-cells covering the villus (a), 

 within which chylous-looking globules have been occasionally seen, when 

 digestion was going on. 



244. Although the Mucous membrane of the intestinal tube is the 

 only channel through which insoluble nutriment can be absorbed in the 

 completely formed Mammal, and the only situation, therefore, in which 

 we meet with these absorbent cells, there are other situations in which 

 similar cells perform analogous duties in the embryo. Thus the Chick 

 derives its nutriment, whilst in the egg, from the substance of the yolk, 

 by absorption through the blood-vessels spread out in the vascular layer 

 of the germinal membrane surrounding the yolk ; which vessels answer 

 to the blood-vessels and lacteals of the permanent digestive cavity, and 

 are raised into folds or villi as the contents of the yolk-bag are diminished. 

 Now the ends of the vessels are separated from the fluid contents of the 

 yolk-bag, by a layer of cells ; which seems to have for its object to select 

 and prepare the materials supplied by the yolk, for being received into 

 the absorbent vessels. 



245. In like manner, the embryo of the Mammal is nourished, up to 



