Experiments on the Early Development of the Amphibian Embryo etc. 617 



philus triseriatus, I was compelled to determine it for myself since 

 this point was essential to the experiments. The development was 

 found to be peculiar in several interesting particulars and was pu- 

 blished in the American Naturalist for Sept. 1896 (50). Briefly 

 the results are as follows: At ordinary temperatures segmentation 

 begins within an hour after fertilization and progresses so rapidly 

 that gastrulation takes place during the first twelve hours, and 

 the tadpole escapes from the egg membranes by the second or third 

 day. There is thus a difference of 25% to SOo/o between the first 

 species, while between the large and small wood frogs it is even 

 more than this, 40 to 50%. 



In tabular form these three species present the following rela- 

 tive rapidity of development, the times given being the average from 

 a large number of observations in each case: 



Species 



Fertili- 

 zation to 

 1st Cleav. 



Ck 



1st 



avage Perio 

 2nd 



ds 



3nd 



Gastr 

 Begins 



ilatiou 

 Ends 



External 

 Gils 



Adult 

 Form 



Amblystoma 

 Eana. . . . 

 Chorophilus . 



lOhrs. 

 3—5 - 

 1—2 - 



llOmins. 

 75 - 

 30 - 



lOOmins. 

 60 - 

 40 - 



lOOmins. 

 50 - 

 30 - 



60hrs. 

 42 - 

 11 - 



78hrs. 

 50 - 

 13 - 



19 days 

 14 - 



31/2- 



100 days 

 70 - 

 30 - 



Methods of Manipulation. 



Since the experiments were to be performed upon eggs in different 

 stages of development no effort was made to fertilize them artificially. 

 They were taken directly from the pools and placed in the solutions 

 in shallow dishes under a receiver. Moistened blotting-paper was 

 put beside them to prevent evaporation with its consequent increases 

 in the percentage of the solution. The latter was also replaced from 

 time to time by a fresh supply in order to secure the best results. 



The eggs were kept in a well lighted room where they received 

 the sunlight about one hour during the day. The temperature was 

 very uniform and stood at about 70 F. 



Before the eggs were placed in the solutions the stage of deve- 

 lopment was carefully determined, and as a further safeguard samples 

 were preserved and afterward sectioned. For hardening Perenyi's 

 weaker fluid was used followed by graded alcohols. 



The author desires to acknowledge his indebtedness to Dr. 

 E. A. Andrews of Johns Hopkins University for the suggestions 



