16 CHARLES F. W. McCLTJRE 



as those described above for Bufo. If a larger number of larvae 

 had been examined, probably the same average results would 

 have been obtained for Rana as for Bufo, with the exception 

 that in Rana, according to Wislocki, no endothelium, except 

 that of the lymphatic system, apparently stores the dye. This 

 is a question, however, which should be further investigated. 



In one of the seven (7) larvae of R. pipiens killed on April 17 

 (6 days in dye) and in four (4) killed on April 18, only the epithe- 

 lium of a few tubules in the pronephros and the stellate cells of the 

 liver capillaries had stored the dye. No trace of dye was observed 

 in any other tissue of the body. In all of the larvae killed on 

 April 19 and 21, dye granules were found in the endothelium of the 

 lymphatics, in addition to the tissues mentioned above. No dye 

 was stored, however, in the epithelium of the tubules in the meso- 

 nephros. See table 4. 



5. EXPERIMENTS TO DETERMINE THE RATE AT WHICH THE STOR- 

 AGE OF DYE GRANULES MAY BE ACCOMPLISHED IN LARVAE OF 

 BUFO WHICH HAVE BEEN PLACED IN A SOLUTION OF COLLOI- 

 DAL ACID DYE AT THE CRITICAL ONTOGENETIC STAGE 



When larvae of Bufo were placed in a solution of colloidal acid 

 dye at intervals soon after fertilization, we have seen that dye 

 granules do not ordinarily become visible in the cytoplasm of the 

 cell, until the ninth day. If the storage of dye granules is associ- 

 ated with the attainment of a distinctive ontogenetic larval stage, 

 and is not influenced by the length of time larvae remain in dye, 

 we might expect the storage of dye granules to be considerably 

 hastened when larvae are placed in dye solutions at the critical 

 ontogenetic stage. 



Experiment 5 (table 5). Forty (40) larvae of Bufo (controls of 

 Experiment 1) were placed hi a 1 :1500 solution of trypan blue on 

 the ninth day after fertilization (June 9) . 



In one (1) larva of this experiment killed on June 9, after five 

 (5) hours in dye and five (5) hours in tap water, and in four (4) 

 larvae killed on June 9, after five (5) hours in dye and twelve (12) 

 hours in tap water, no dye granules were observed in the cyto- 

 plasm of any cell hi the body. 



