BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 47 



A communication has been established at the hepatico-sub- 

 cardinal junction between the liver circulation and the right sub- 

 cardinal vein, so that the postcava is now definitely formed. This 

 communication is quite insignificant, however, and most of the 

 blood from the posterior regions still passes to the heart by the 

 postcardinal veins. 



The thyroid glands of the right and left sides are still connected 

 posteriorily. The tubules of the pronephros have increased hi 

 number and three nephrostomes are formed. This is the same 

 number of nephrostomes found in Bufo on the ninth day after 

 fertilization. The right mesonephros is represented by six renal 

 vesicles and the left by five. The vesicles of the right side are 

 larger than those of the left. Some of the former are hollow but 

 none of them connect with the pronephric duct. 



The external gills are still highly developed and their capillary 

 circulation is in full swing. The blood-vascular loops of the tail 

 now reach about half-way into the caudal fin. No lymphatics are 

 present in the caudal fin. In none of the larvae was dye observed in 

 the intestinal canal. 



The external gills begin to atrophy in Bufo between the sixth 

 and seventh days after fertilization and are completely lost in 

 most cases at the beginning of the seventh day. As observed by 

 Hoyer ('08), one can then more readily observe the rhythmical 

 contractions of the anterior lymph-hearts. Hoyer has stated that 

 the formation of valves in the lymph-heart coincides in the frog 

 with the loss of the external gills. In B. lentiginosus the external 

 gills are still present when the valves are formed sometime between 

 the fifth and sixth days. 



From the sixth day on up to the ninth day after fertilization, 

 when direct evidence of phagocytosis may ordinarily be first 

 observed in certain cells, there is naturally a gradual and pro- 

 gressive increase in the amount of lymph which passes from the 

 periphery to the veins. 



The above observations decidedly indicate that a continuous 

 lymph flow from the intercellular tissue spaces of the head region 

 to the venous circulation, is inititated in the toad embryo some- 

 tune between the fifth and sixth days after fertilization. Prior to 



