B. - tWn. 



n ho have not follow* d 

 the sul efully. However, dow thai the origin and method of 



ivth of tin' lymphatic system has been cleared up, bo that the funda- 

 mental morphology is understood, the controversy has had this great 

 value, tlint it has brought up for analysis and discussion every con- 

 ceivable method of growth. Lymphatics do nol arise as dilated per- 

 ipheral tissue - ifter the manner of the ccelom as the earlier 

 embryologis ght; they do not grow by the addition of holloa con- 



ssue cells, as Schwann and Virchow thoughl ; they do n 

 as perineural spaci s, uor bj ition of a vein, aor by extra-intimal 



fts, nor by the pi re addition of connective tise ces, nor 



by the addition of detached blood vi --■ Is, but they bud from the vi 

 and grow by the sprouting of their endothelial wall. 



IX. CONCLUSIONS. 



most important result of this study on the morphology of the 

 lymphatic system is the emphasis it throws on the importance of 

 endothelium as a tissue. The angioblast is one of the earlj 

 to ■ entiated ; ii is nol an inert lining Eor vessels, but an activi ly 



iwing functioning tissue. In its place of growth it is a syncytium 

 of actively amoeboid protoplasm. Mollier (99) has shown that in the 

 spleen it may be reticular; Mall (86 and 87) has shown that it may 

 give rise to reticulum. Undoubtedly the further development «{ our 

 knowledge of endothelium depends on the development of the new 

 experimental anatomy. 



lymphatic endothelium buds off from the veins. It is always 

 a little different in appearance from the endothelium of the veins, and 

 the lymphatic capillary is different in size and form from the blood 

 capillaries. The growing lymphatic tip has the remarkable character- 

 istic that it avmd- the blood capillaries, while it i- attracted by other 

 lymphatic capillar] 



Endothelium i- the essential tissue of the lymphatic system. In the 

 lower • es lymph hearts are formed by the addition of striated 



muscle t<> primary lymph sacs. In the higher forms lymph glands 

 formed by the development of lymphocytes around the ducts. 

 This take- place not only in the wall of the primary lymph sacs, 

 along plexuses of 3, so that there are primary and secondary 



lymph glan 



