BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 51 



that they are an independent tissue, growing by division of primary 

 lymphatic endothelium, and invading the embryonic body, as a vine 

 climbs a trellis. 



These three views, as they apply to the tadpole, can be subjected to a 

 crucial test* in the light of the discovery that try pan-blue is an elective 

 stain for amphibian embryonic lymphatic endothelium. Experiments 

 necessary to this end are being prosecuted in this laboratory. Even at 

 the present time, while these experiments with vital dyes are only in 

 their initial stages, it is possible by their help to draw certain funda- 

 mental conclusions, which may aid in directing the study of lymphatic 

 growth. 



The view maintained by a second group of writers, namely, that 

 lymphatics grow by the 5 .... transformation of mesencnyme 

 into endothelium, clearly becomes untenable, since mesenchyme and 

 lymphatic endothelial cells are shown by their reaction toward the dye 

 to be biologically different; and conversion of one into the other be- 

 comes extremely improbable. 



The observations made so far upon vitally stained larvae, sub- 

 stantiate and add additional proof to the interesting observations of E. 

 R. f 'lark on the growth of lymphatics in the tadpole's tail. The author 

 is able to confirm Clark's view that these lymphatics grow only by 

 sprouting, and by sending out fine protoplasmic processes, which gradu- 

 ally become definite lumen-containing sprouts. 



Let us now see to what extent Wislocki's method of vitally 

 staining the lymphatics really contributes evidence, as he claims, 

 that the lymphatics of the frog are derived from the endothelium 

 of the veins. 



Evidence from the standpoint of vital staining by colloidal acid 

 dyes that the lymphatics grow out from the veins, would at least 

 call for the demonstration of an early stage of growth, at which a 

 vitally stained lymphatic is in the process of growing out from a 

 vein. I may state that not even the faintest approach to such a 

 demonstration can possibly be realized either in the embryo of the 

 frog or toad. The reason for this is plain. The lymphatic system 

 of the frog and toad does not become vitally stained, so to speak, 

 by colloidal acid dyes, until an extensive system of continuous 

 lymphatic vessels have been formed, which convey lymph from 

 practically all regions of the body to the anterior lymph-hearts and 



4 Italics added by the writer. 



5 The portion omitted from the quotation refers to extraintimal and perineural 

 lymphatic spaces which thus far have not been observed in the frog or toad. 

 (McClure, '15, p. 66.) 



