8 DXTBLDC TJICrVERSITT. 



of the very first conditions necessary for the development, — for the life 

 of the tadpole. Even when respiration is performed by the external 

 gills and cutaneous surface, life is very short, if the creatures have not 

 access either to the surface, or at least a very highly aerated water ; 

 and in all cases life is of limited duration when the animals are prevented 

 from coming to the surface of the water in which they live. Higginbot- 

 tom's observations agree on this subject; he says: " I found that the 

 tadpole of the frog soon dies in either aerated or boiled water, if excluded 

 from atmospheric air ; those in aerated water live longest, some of them 

 I found at the top of the water, and on examination the lungs were ob- 

 served to be inflated, whilst those tadpoles in the boiled water sank to 

 the bottom of the vessel. Tadpoles put into boiled water, exposed to 

 the atmospheric air, live as in aerated water. 



"W. E. Edwards seems to have been in some degree blinded by his 

 apparent anxiety to prove that light was an important agent in bringing 

 about the transformation of the tadpole. Neither Higginbottom's re- 

 sults nor mine accord with his, when he says that he ''put some tad- 

 poles of the frog into two large vases containing ten litres of water, both 

 capable of admitting light, the one of glass, but with a diaphragm on 

 the surface of the water to prevent aerial respiration ; the other open so 

 as to leave to the animals the liberty of rising to the surface and breathing 

 atmospheric air. Both sets enjoyed the light ; there was no difference 

 seen in the want of pulmonary respiration. Those that were deprived of 

 it (indeed, more slowly) became transformed, but this delay was so short 

 that the influence of the cause, which I wished to appreciate, appeared 

 very feeble.* 



Sixth Experiment. — Two glass jars, of the same dimensions and form 

 as in the first experiment, were filled with fresh water, and 100 

 healthy tadpoles were put in each. One (B) of these was placed in 

 the window; the other (B f ) was put into a chest in darkness, but in the 

 same apartment, and consequently nearly the same temperature. Neither 

 set were supplied with any food, but it must be remembered that they 

 ate voraciously their dead companions, and that the vegetable growth 

 which rapidly appears in water standing exposed to light gives abun- 

 dant nutriment to those submitted to light. This experiment was com- 



* W. F. Edwards, " De 1'Influence des Agens Physiques sur la vie," page 398-9. 



