GENERAL PHYSIOLOGY OF THE EPITHELIUMS. 205 



really holes, by means of which the two sides of the mesen- 

 tery are brought into communication with each other. 

 These orifices appear to resemble in structure those which he 

 has described as belonging to similar parts of the epiploon. 

 (For particulars, see Ranvier, " Soc. de Biologie," 1872, and 

 H. Farabeuf, "De 1'Epiderme et des Epitheliums," p. 171.) 



We may conclude from this that the connective tissue 

 represents one of the principal origins of the lymphatic sys- 

 tem, and that the loose cellular tissue may be considered as a 

 vast lymphatic chambered sack, communicating directly with 

 the lymphatic vessels. Pathological anatomy furnishes 

 numerous proofs of this (Ranvier), as well as comparative 

 anatomy, and the study of the development of the lymphatic 

 vessels, and of the tissues called lymphoid tissues: thus the 

 boundaries between the sacks or lymphatic reservoirs of the 

 inferior vertebrated animals and the surrounding connective 

 tissue are scarcely marked, and Meyer considers the former 

 lacunas of cellular tissue (frogs). As we ascend the scale of 

 the vertebrated animals, and find that the lymphatic system 

 which exists in a distinct form only in these animals, is more 

 and more clearly developed, we see that it arises from modi- 

 fications of the connective tissue: Leydig found the adventi- 

 tious tunic of the vessels of the mesentery in many bony fish 

 transformed into areolse filled with small colorless cells, that 

 is, really, into a genuine lymphatic sheath ; the same phe- 

 nomenon is observed in the adventitious tunic of the arteries 

 of the spleen, the connective tissue of which changes grad- 

 ually into this lymph oidal reticulum, which constitutes the 

 corpuscles of Malpighi and the lymphatic ganglions. 



The structure of the lymphatic ganglions is the last proof 

 which we shall mention of the close connection between the 

 lymphatic system and the connective tissue. These gan- 

 glions, into the histological study of which we cannot now 

 enter, have been always justly considered as formed by the 

 clustering of the lymphatic capillaries (see page 199) ; close 

 investigation has lately shown that they are essentially com- 

 posed of connective tissue whose meshes are more or less 

 free, and in which (lymphatic lacuna) the lymphatic current 

 is diffused, drawing with it the lymph corpuscles (page 

 198) which are developed in it by proliferation of the plasrnic 

 cells, exactly as the globules of pus are developed by similar 

 proliferation in any inflammation of the connective tissue : 

 this explains the resemblance, or rather, the morphological 

 identity, of the pus globules and the lymph or white globules 

 of the blood. 



