LYMPHATICS IN FROG LARVAE 37 



5. The same conclusions as have been proposed for the 

 formation of the larger veins in plexuses apply also to the 

 long ducts of the lateral lymphatics. 



6. Though two parallel lines of vessels do precede the 

 appearance of the main dorsal trunk, the latter is not typi- 

 cally formed by fusion of two bilateral trunks, but is a favored 

 path resulting from the physiological conditions acting on 

 the plexus. 



7. The peripheral lymph vessels, outgrowths of the plexuses 

 of the early system, follow the segmental pattern of the veins 

 as in urodeles; but their main collecting ducts, dorsally and 

 laterally, furnish from the first a more direct and quicker 

 path for the flow of lymph from the tissues to the primitive 

 kidneys than is provided by the veins. This agrees with the 

 earlier suggestions of the probable causal nature of the rela- 

 tions revealed in the development of lymphatics, kidneys, and 

 progressive tissue changes. It seems to point to a need for 

 the elimination of substances which might otherwise accumu- 

 late harmfully in the tissues (Abel, '12). 



8. Drinker ('33, '38) after recent experiments on adult 

 frogs proposes as the fundamental function of the lymphatic 

 system, a constant returning to the blood of proteins which 

 accumulate in the tissues. 



Whether this is the only function of the system further 

 experiments can alone decide; the fact, shown by injection, 

 that lymph bathes the tubules of the pronephros of frog larvae 

 so profusely and constantly on its way to the heart suggests 

 strongly some elimination here, in addition to the mere return 

 of protein to the blood. 



FINALLY, CERTAIN STATEMENTS WILL BE REPEATED HERE, 



BECAUSE OF THEIR BEARING ON THE DISCUSSION 



WHICH FOLLOWS (pp. 40-45) 



A statement on the origin and primary stages of lymphatics 

 in frog embryos may be expressed best in words from the 

 report which was presented, with demonstrations, before the 

 American Association of Anatomists, December, 1913, and 



