ORIGIN OF LYMPHATICS IN BUFO 181 



origin of lymphatic channels from a few very definite centers in 

 the organism has been too dogmatically asserted, and those 

 investigators who have strongly adhered to it now find it difficult 

 to consider exceptions, which, there is a probability, may prove 

 the rule. In an analysis of the researches on the genesis of the 

 lympathics we do not find a single really valid objection, based 

 on correct interpretation of observations, to discredit the view 

 of the origin of a lymph duct from a number of points, that is, 

 from mutliple anlageii, which in toad embryos are proliferated 

 from the intima of the vein which the definitive duct accompanies. 

 The present findings, in Bufo, then, will permit of a partial 

 acceptance of both the "centrifugal growth theory" and the 

 "discontinuous, in situ mesenchymal origin" of lymph ducts. 

 That the lymphatic endothelium, here considered, arises from 

 venous endothelium has been shown beyond the shadow of a 

 doubt, and the writer consistently, though tentatively, abandons 

 the hypothesis of its derivation in other vertebrates from mesen- 

 chj^mal cells, unless their lympathic system is shown to behave 

 differently, which is scarcely conceivable. But the other tenets 

 of the 'outgrowth theory,' such as continuity and centralization 

 in lymphatic development, he can not accept, for the present 

 observations reinforce strongly the diametrically opposite doc- 

 trines of discontinuity and multiple origin. The ventral cephalic 

 lymph sinus is a product of the walls of the external jugular 

 veins; its anlagen arise not at one point but individually at 

 intervals along the entire extent of the cranial division of these 

 veins. E\'en after the lymph sinus has become a single chamber 

 by the coalescence of its rudiments, it remains as a blind reservoir 

 until a relatively late stage when it joins the lymph hearts. The 

 lateral lymphatic ducts of the trunk, too, do not spring from one 

 center but are formed and acquire continuity by the fusion of a 

 number of anlagen, which originate along the postcardinals and 

 their dorsal tributaries, the intersegmental veins. To satisfy 

 the 'outgrowth theory,' the lymphatic vessels mentioned, the 

 sinus and at least the anterior half of the lateral ducts, should 

 develoji as continuous growths from the anterior lymph hearts. 



