AND OF LIGHT. 



225 



in temperate climates, or in temperate and arctic ones, 

 be borne in mind. 



Some striking observations on the effects of tempera- 

 ture on growth were made by Higginbottom some fifty 

 years ago.* Ova of the frog were allowed to develop 

 under otherwise similar conditions at the temperatures 

 15.6, 13.3, 11. 7, and 10.5 C. The tadpoles were 

 observed to leave the ova respectively 9, 14, 20, and 20 

 days after the beginning of the experiment, whilst 

 frogs were fully developed after respectively 72, 160, 

 170, and 234 days. Thus a difference of 5 C. more 

 than trebled the period of development. 



Within the last few years, a considerable number of 

 observations have been made. Thus Lillie and Knowl- 

 ton t experimented with the ova of Amblystoma tigri- 

 num and of the frog Rana virescens. The time of de- 

 velopment from the first or second cleavage to the last 



*Phil. Trans. 1850, p. 431. 



Zool. Bulletin, vol. i. p. 179. 



