756 PROCEEDINGS OF THE ACADEMY OF [DeC, 



But after 2 o'clock the hour's shutting away from the light brought 

 about an apparently normal spawning. I found that the with- 

 drawal of light brings about surprisingly definite results. The 

 condition of the tissues arrives at the point requisite for the release 

 of the eggs almost on the minute. This constancy is not appre- 

 ciably affected by moderate changes in Ihe temperature. A large 

 number of experiments and observations have been made to educe 

 the exact time of stimulation (if we may so speak of an influence 

 which seems to be purely negative) and the results are summarized 

 in the following table. Record was kept of experiments carried 

 on during the whole of the fertile season, partly in one summer, 

 paiUy in the next. The stimulation -time varies somewhat with 

 the season ; the table gives the results obtained during the last week 

 in July, when the eggs were being discharged in the greatest 

 numbers. 



As the hour approached the normal time for the deposition of the 

 eggs, the precision with which they were discharged became more 

 and more marked. Between 4 and 7 P.M. the lime of darkening 

 necessary to produce spawning does not vary more than four minutes 

 on either side of the hour. 



Some experiments were tried with a view to inhibiting the normal 

 deposition of eggs, or at least of hindering it, by keeping the eggs 

 in strong artificial light. The results were not conclusive, as the 

 electric lights in the laboratory were not in use until after dusk, 

 when part of the stimulus had already been received. The experi- 

 ments showed a certain degree of retarding of the process of spawn- 

 ing as a result of the strong illumination. It would be interesting 

 to determine whether the use of stronger light, applied at the 

 commencement of evening dusk, would result in complete inhibi- 

 tion of the process.^ 



^ Subsequent experiments show that brilliant illumination has a stupe- 

 fying eflfect on medusa?, inhibiting contraction of the bell and almost 

 preventing spawning, though not altogether or in all instances. 



