BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 13 



1 . Pronephros. Dye granules were found in the epithelium of the 

 proximal portion of some of the tubules in the pronephros. In 

 a few larvae the pronephric epithelium was the only tissue in the 

 body in which the dye had been stored. The tubules which are 

 the first to store the dye occupy a dorsal and lateral position in 

 the pronephros. The epithelium of the pronephric (Wolffian) 

 ducts and nephrostomal canals does not store the dye. 



2. Epithelium of pharynx. Dye granules were found in thick- 

 ened patches of epithelium which occupy a caudal and lateral 

 position in the roof of the pharynx. They were also present in the 

 epithelium covering a prominent fold which projects laterally, on 

 each side, from the floor of the pharynx, near the caudal end of the 

 tongue anlage. These epithelial areas of the pharynx, like the 

 epithelium of the pronephric tubules, function as important 

 regions for the deposition of dye particles. This function of the 

 pharyngeal epithelium can be especially well demonstrated in 

 much older larvae which have been subjected to a long immersion 

 in dye. 



Although the absorption of dye particles by such tissues as 

 pharyngeal and pronephric epithelium may not be regarded in 

 the same light as their ingestion by macrophages, it is an inter- 

 esting fact that both processes are initiated in the embryo at the 

 same time and in association with the attainment of the same 

 ontogenetic larval stage. 



3. Stellate cells of the liver capillaries (Kupffer's cells). Dye 

 granules were found in the cytoplasm of the endothelial cells 

 which line the venous capillaries of the liver (stellate cells of v. 

 Kupffer). The parenchyma of the liver was never observed to 

 house the dye nor even to be diffusely stained in larvae which had 

 remained in tap water for some time before killing. In one in- 

 stance Kupffer's cells were found to be the only cells in the body 

 which had stored the dye in the form of granules. The possible 

 significance of this condition will be considered in connection 

 with another topic (Chapter 9). 



4. Endothelium of the lymphatic system. Dye granules were 

 stored in the endothelium of all the lymphatics, except in that 

 which lines the anterior lymph-hearts. The endothelium of the 



