BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 15 



It is quite probable that the phagocytic character of the lym- 

 phatic endothelium observed in certain fishes (Wislocki, '17) and 

 amphibia, may be correlated with the absence of lymph glands in 

 these animals. A comparative study of the conditions observed 

 in the embryo and adult of vertebrates in general might lead to 

 interesting conclusions. 



6. Free cells. Free cells containing dye granules were rarely 

 found in Bufo on the ninth day after fertilization. A few mono- 

 nuclears 3 containing dye granules were found in the mesenchyme, 

 mesentery, intertubular tissue of the pronephros and in one in- 

 stance in the portal vein. A few cells much larger than the mono- 

 nuclears and usually of irregular form, were being desquamated 

 from the endothelium of the cephalic lymph sinuses in some of the 

 larvae killed on the ninth day after fertilization. These cells were 

 loaded with dye granules and were found in the cephalic lymph 

 sinuses and in the neighboring mesenchyme. 



No trace of dye, in the form of granules, was observed in the 

 tissues of twenty-nine larvae of Bufo killed on the ninth day after 

 fertilization, other than those mentioned above. 



The left mesonephros is not developed to any extent in Bufo 

 lentiginosus on the ninth day after fertilization, and not a trace 

 of dye was housed in the epithelium of the right mesonephros at 

 this time. None of the red blood-cells, the thymus or thyroid 

 glands, nor any of the tissues of the nervous system contained a 

 trace of dye. No indication of the anlage of the spleen can be 

 observed at this time. 



Observations on the larvae of Rana pipiens (table 4) killed at 

 the critical stage, are unfortunately not as extensive or as detailed 



1 The term mononuclear leucocyte is applied here and in all subsequent cases 

 mentioned in this paper, to cells essentially similar to those figured by Kliene- 

 berger and Carl as "Mononuklearer L" and "Eingeschnurter mononuklearer L" in 

 their treatise entitled "Die Blut-Morphologie der Laboratoriums-Tiere," Leipzig, 

 1912. (Tafel XII, 7 and 8 in fig. 1.) 



Mononuclear leucocytes with eccentrically situated oval nuclei appear to be the 

 chief free macrophages found in the tissues of anura which most readily react 

 toward colloidal acid dyes. In later larval stages and in the adult they are found 

 in abundance in the tissues of the frog and toad where they take up colloidal acid 

 dye particles with great avidity. 



