BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 49 



deposition might possibly be somewhat hastened, if dye solutions 

 of higher concentration were used. (Compare Exp. 10 c and 11). 

 In any event, however, dye could not reach the general circula- 

 tion from the tissue spaces of the head region by the lymphatics 

 until the cephalic lymph sinuses had established their connection 

 with the veins. 



The above observations seem to confirm a recent observation of 

 the writer concerning the establishment of a continuous lymph 

 flow between the tissue spaces and veins in the embryo of the 

 trout (McClure, ; 15a). 



It was found prior to about the twenty-second day after fer- 

 tilization in the rainbow and steelhead trout, that the lymphatics 

 of the head and pharynx are represented by a discontinuous sys- 

 tem of independent and disconnected anlages which consist 

 largely of endothelial-lined vesicles or sacs. Two of these inde- 

 pendent anlages, the subocular lymph sacs, are relatively huge 

 structures situated ventral to the eyes which can be observed, 

 injected or otherwise experimented on in the living embryo. 

 During then* independent stage these sacs collect transudated 

 lymph from the tissue spaces and store it temporarily until they 

 establish a connection with the lateral pharyngeal lymphatic, 

 through which they then drain into the veins. At this time also 

 valves begin to be formed between the lymphatics and the veins 

 (McClure, '15). 



It will be observed that a continuous lymph flow between the 

 head sinuses and the veins is initiated in the same manner in the 

 embryo of the toad and the trout, by a confluence between the 

 independent head sinuses and the lateral pharyngeal lymphatic 

 (ductus cephalicus of Hoyer). Whether the head sinuses in Bufo 

 also collect transudated lymph from the tissue spaces, prior to 

 the time they drain into the veins, has not been definitely deter- 

 mined up to the present time. 



It might be possible by means of subcutaneous injections of 

 dye solutions into trout and chick embryos, to confirm the above 

 observations made on the toad. If the principle outlined above for 

 the toad is correct, one would expect it to be so in all cases. 



MEMOIR NO. 8 



