QO ELEMENTS OF HISTOLOGY. [Chap. xi. 



corpuscles, and other formed matter, are readily taken 

 up by the stomata (see Fig. 20) and brought into the 

 lymphatics, and in this the respiratory movement of 

 the intercostal muscles, of the diaphragm, and of 

 the lungs respectively, produces the result of the 

 action of a pump. 



118. There is a definite relation between the 

 lymphatics and the epithelium covering the mucous 

 membranes and lining the various glands and between 

 the endothelium covering serous membranes and that 

 lining vessels and lymph cavities viz., the albumin- 

 ous semifluid cement substance (see former chapters) 

 between the epithelial and endothelial cells is the 

 path by which fluid and formed matter pass between 

 the surfaces and the lymph-canalicular system, the 

 latter being the rootlets of the lymphatics. 



119. Lymph taken from the lymphatics of dif- 

 ferent regions differs in composition and structure. 

 That from the thoracic duct contains a large 

 amount of colourless or white corpuscles lymph cor- 

 puscles each of which is a protoplasmic nucleated cell 

 similar in aspect and nature to a white blood corpuscle. 

 They are of various sizes, according to the stage of 

 ripeness. The smaller contain one, some of the larger 

 contain two and three, nuclei. The latter show more 

 pronounced amoeboid movement than the small ones. 

 A few red corpuscles are also met with. Granular 

 and fatty matter is present in large quantities during 

 and after digestion. 



In the frog (and also in other lower vertebrates, 

 e.g., reptiles) there exist certain small vesicular lymph 

 cavities, about an eighth of an inch in diameter, 

 which show rhythmic pulsation ; they are called lymph 

 hearts. On each side of the os coccygis and underneath 

 the skin is a pulsating posterior lymph heart. The 

 anterior lymph heart is oval, and situated on each 

 side between the processus transversus of the third 



