i] PERIODICITY IN CONVOLUTA 31 



for a fuller physiological analysis of the mode of 

 reaction of protoplasm to physical stimuli. 



The problem with respect to periodicity of egg- 

 laying by Convoluta requires us to ascertain whether 

 it is possible to refer the periodicity to any definite, 

 recurrent physical condition of the natural environ- 

 ment of the animal. 



The facts about to be related appear to indicate 

 that this is possible. 



It may be premised that if adult C. roscoffensis 

 are kept in darkness for some time previous to the 

 full development of their eggs, no egg-capsules are 

 laid. The lack of egg-production on the part of 

 dark-kept animals is due to the fact that animals 

 kept under such conditions become starved and, as 

 a consequence, incapable of supplying the eggs with 

 food-materials. But if a similar experiment is made 

 with animals containing eggs in an advanced stage of 

 development and already supplied with plenty of 

 food-materials, it is found that the number of egg- 

 capsules produced by animals kept in darkness is 

 actually greater than that produced by animals which 

 are exposed throughout the day to the light. Hence 

 we may infer that exposure to long spells of twelve 

 or more hours of light is unfavourable to the maturing 

 or deposition of eggs. Further experiments on similar 

 lines show that egg-laying reaches its maximum when 

 the animals are subjected daily to one short spell of 



