28 THE ROYAL SOCIETY OF CANADA 



found that in a species of Obelia more hydranths regenerated in the 

 dark than in daylight during the same time, and in the regeneration 

 of single hydranths a larger number of annuli was produced in dark- 

 ness than in daylight. It has long been known that so long as accumu- 

 lated foods material last the growth of plants is greatly accelerated 

 in the dark. Also Downes and Blunt (1877, p. 496) found that 

 "light is inimical to the development of bacteria and the microscopic 

 fungi associated with putrefaction and decay," and that "under 

 favourable conditions it wholly prevents that development." This 

 effect of light on plants is therefore observable in the case of the 

 mussel as well as in Obelia, and is doubtless very general among 

 marine animals. The occurrence of many attached marine animals 

 only on the lower surfaces of stones or in similarly protected situations 

 when in shallow water has been perhaps generally explained as due 

 to their avoidance of the light. In the experiment described the two 

 species of hydroids grew in the middle compartment of the "dark" 

 box only. The true explanation may be that in direct sunlight they 

 are not only retarded in growth, but actually killed off. 



Downes, A . and Blunt, T. P. 



1877. Researches on the effect of light upon bacteria and other 

 organisms. Proc. Roy. Soc, Vol. XXVI, pp. 488-500. 



Higginbottom, J. 



1850. Influence of physical agents on the development of the 

 tadpole of the triton and the frog. Phil. Trans. Roy. Soc, 

 pp. 431-436. 



Torrey, H. B. and Martin, A. L. 



1910. The Effect of Light upon the Growth and Differentiation 

 of ObeHa. Proc. 7th Int. Zool. Congr., Boston, p. 277. 



