The Origin and Development of the Lymphatic System. 73 



figs. 1, 2 and 3 the simple hypothesis of Banvier, shown in fig. 18. 

 This indicates that lymphatics bud off as lymphatics from the veins 

 and have the same relation to tissue spaces as have blood capillaries. 



The most difficult obstacle in regard to this theory is what we call 

 Mayer-Lewis anlagen. Mayer (89) noted in the tadpole's tail certain 

 isolated vessels which he thought were evidences of the degeneration 

 of blood vessels. 



Eanvier (114, p. 578) in studying the plexus of lymphatics of the 

 great omentum in a new-born cat noted that a great many of the 

 vessels terminated in cul de sacs. Some were attached by extremely 

 slender threads, so that they looked as if they were becoming iso- 

 lated by the atrophy of the intermediate part. Since in the adult cat 

 there are no lymphatics in the omentum, Eanvier interpreted this as 

 a method of degeneration of lymphatic vessels. 



The study of the method of degeneration of blood and lymphatic 

 capillaries is an important one. It is obvious that there must be a 

 destruction of capillaries, since a single vessel or a few vessels come 

 from a plexus of capillaries. In Clark's observations (25, p. 191) the 

 usual method of degeneration is by retraction of the processes, but 

 he has also observed (26, p. 410) together with Mayer and Eanvier, 

 that an occasional segment of a blood capillary or lymph capillary 

 may become detached and be left to atrophy. This is in accord with 

 some of the findings of pathology. We must, therefore, conclude that 

 detached, degenerating vessels do occur, though they do not represent 

 the usual method of degeneration. 



E. T. Lewis (76) found that in reconstructions lymphatics looked 

 like chains of beads, and to explain this phenomena he suggested that 

 lymphatics might grow by small detached portions of blood vessels. 

 These hypothetical lymphatic anlagen we call Lewis anlagen. 



It is clear in watching lymphatics grow, that they never pick up 

 isolated vessels, but grow by the increase in the protoplasm of their 

 own wall ; yet it is clear also that reconstructions of uninjected lym- 

 phatics appear like rows of beads. 



To study this point it was necessary to submit the method of recon- 

 struction to comparative tests with the method of injection and when 

 possible with the method of growth in the living form. This has been 

 done three times (Clark, E. E. 26; Clark, E. L. 27, and Sabin 135). 



The best opportunity for studying this point is the tadpole's tail, 

 where, in the living specimen, or in the tail fixed in alcohol, the entire 



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