BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 7 



of the lymphatics has stored the dye, the dye granules could not 

 be as distinctly observed as in the living animals. 



Experiments with trout and other fresh water teleost embryos 

 show that when placed in colloidal acid dye solutions, the latter 

 do not, as in amphibian larvae, gain entrance to the body and 

 vitally stain the tissues. As observed by Wislocki ('16) for Hyla, 

 the larvae of Acris are also less immune to the toxic action of 

 these dyes than those of Rana and Bufo. 



All of the microscopic observations referred to in the following 

 pages were made with a Zeiss homogenous oil immersion objective 

 (2 mm. apert. 1.40) and appropriate oculars. 



3. ON THE DETERMINATION OF THE EARLIEST STAGE OF LARVAL 



DEVELOPMENT IN BUFO AND RANA, AT WHICH CERTAIN 



TYPICAL TISSUES ARE FIRST OBSERVED TO REACT 



TOWARD COLLOIDAL ACID DYES 



Experiment 1 (table 1). Ova of Bufo lentiginosus were fertilized 

 in the morning of May 31 and the first body movements observed 

 in the evening of June 2. These larvae averaged four millimeters 

 in length in the morning of June 3, at which time the external 

 gills had not yet made their appearance. In the morning of June 

 3, the third day after fertilization, seventy-six (76) larvae were 

 placed in a 1 : 1500 solution of Niagara blue (dye No. 161) made 

 up with tap water, and were allowed to continue their develop- 

 ment at ordinary room temperature. A certain number of larvae 

 were removed daily from the dye solution from June 4 to June 14, 

 inclusive, and, in each case, were transferred to tap water, in 

 which they remained twenty-four hours before killing and fixa- 

 tion. Since the dye taken up by the circulation continues to act 

 on certain tissues even after larvae have been transferred to tap 

 water, the duration of its action is necessarily estimated in these 

 experiments, from the time larvae are first placed in the dye 

 until the time of killing and fixation. For example, the twelve 

 larvae killed on June 9, referred to in column V of table 1, were 

 placed in the dye solution on June 3, transferred from the latter 

 to tap water on June 8 and killed on June 9. Experiment has 



