1/8 MAX MORSE. 



the larger vessel was filled with water so that the fingerbowl 

 was submerged to a depth of fifteen centimeters. The apparatus 

 was placed in the direct sunlight, which fell upon it from eight 

 o'clock in the morning until about four thirty in the afternoon. 

 The temperature of the water was kept at 20 C. It was not 

 possible to reduce the temperature of the water, under the cir- 

 cumstances, below this. Control specimens were placed in a 

 similar vessel, somewhat smaller, in the shadow near the larger 

 one. The first hydranths fell from the individuals in the larger 

 vessel,- exposed to the rays of the sun, during the third day. 

 Those in the control gave evidence of autotomy at about the same 

 time, or even earlier, perhaps. This result is quite similar to 

 that given by colonies of Tubularia brought into the laboratory 

 and placed in running salt water either in the light or in the 

 dark. It seems to point to the absence of any effect of sunlight 

 in inducing the process of autotomy. The hydranths very prob- 

 ably would have remained longer if the temperature could have 

 been reduced, as is shown in other experiments to be described. 



In another set of experiments fingerbowls of specimens were 

 placed in a trough of chipped ice and set in the direct sunlight. 

 The hydranths were retained for nearly two weeks. In a third 

 set, under more natural conditions, stems of the hydroid were 

 tied to weighted blocks of wood and these were submerged about 

 fifteen centimeters beneath the surface of the water in the " outer 

 pool " of the Bureau of Fisheries at Woods Hole, where the tide 

 sweeps through at all times, bringing cool water from Vineyard 

 Sound and Buzzards Bay. The individuals, of course, were 

 subjected to the direct rays of the sun. The hydranths were 

 retained for two weeks and this would have continued undoubt- 

 edly if the waves during a stormy period had not torn the speci- 

 ments from their supports. The average daily temperature of 

 the surface water during this time of year was 19 C. At night 

 the temperature fell to 15 C. 



We may conclude from these experiments that sunlight is not 

 a factor in producing autotomy in Tttbuloria. 



With respect to darkness, data have been given already to 

 show that this is not a potent factor. In the case of hydranths 

 placed in the ice-chest, the individuals were not exposed to light 



