532 



and amidic acids. But they may be, as I have pointed out, inter- 

 preted in another way. The question thus presented is accessible to 

 experiment, being capable of solution in a variety of ways ; and it 

 appears useful to postpone further speculation upon this subject until 

 it may be raised upon a broader experimental foundation. 



II. " Additional Observations and Experiments on the Influence 

 of Physical Agents in the Development of the Tadpole 

 and the Frog." By JOHN HIGGINBOTTOM, Esq., F.R.S. 

 Received Dec. 24, 1861. 



In a former paper " On the Influence of Physical Agents on the 

 development of the Tadpole of the Triton and the Frog," which the 

 Royal Society honoured with a place in the Philosophical Transac- 

 tions for 1850, experiments were detailed to prove that the ovum of 

 the frog (the Rana temporaria) underwent its metamorphosis in the 

 absence of light, contrary to the experiments of Dr. W. F. Edwards 

 of Paris, related in his work ' On the Influence of Physical Agents 

 on Life.' 



My most satisfactory experiment was made in a rock cellar 30 

 feet deep, where no solar light ever entered ; the mean temperature 

 of the cellar was 5 1 Fahr., I believe, the lowest temperature at 

 which the transformation could be effected. 



The ova of the frog, just deposited, were placed in the cellar on 

 the llth of March, and on the 31st of October the first was fully 

 developed in the form of a frog ; while other ova deposited on the 

 same day, which were placed in a shady part of a room at 60 Fahr. 

 and covered with several folds of black calico, were fully developed 

 on May 22nd, twenty- three weeks earlier than those in the cellar. 



The experiment proved that the development of the frog depended 

 upon the temperature, and not upon the presence of light. I found 

 by other experiments that those in the light, and those deprived of 

 light, were equally developed if placed at the same temperature. 

 I observed that an excess of light retarded the development. 



1. On the Influence of Light on the Ovum. 



My former experiments not being parallel with those of Dr. Edwards, 

 I was desirous of following his steps. Dr. Edwards says, in his work 



