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DUBLIN UNIVERSITY 



having the opercula of the gills still open, and fit for aquatic respiration. 

 In C one continued alive, but eventually died undeveloped. 



The following Table shows the rates of mortality in Experiments, 1, 

 6, and 7, in which vessels of the same form and capacity were used, 

 and the same number of tadpoles put in each : — 



It will be observed that in all these experiments the mortality was 

 at first much greater in those exposed to the light than among those in 

 darkness. The reason of this is sufficiently obvious in the first experi- 

 ment, where the animals are prevented by a diaphragm from coming to 

 the surface, for those in the light, being much more active, lively, and 

 vigorous in their movements than those in the dark, became sooner ex- 

 hausted from want of abundance of oxygen. In the other experiments 

 this phenomenon is not as easily explained. 



In the seventh experiment only did any become developed into 

 frogs, and this was not only where they were exposed to light, but 

 where from the beginning they were specially fed. Before attempting 

 to give what appears to me to be the explanation why, in the experi- 

 ments before us, so small a number as two only became frogs, let me 

 say what is in this country the usual condition in the natural state of 

 the tadpole, which I have often carefully observed. The instinct of 



