IOO THURLOW C. NKI.SuV. 



floating laboratory in water with a temperature of 3 C. Several 

 .mim.ils were at once dipped up to make certain that the swim- 

 ming plates were actually in motion. 



To determine the minimum temperature at which the paddle 

 plates would beat in winter, on January 19, 1924, I took Mnemi- 

 opsis from the water beside the laboratory at a temperature of 

 4 C. With the aid of a pack of ice and salt the water containing 

 the animals was cooled down until at 0.7 C. water and cteno- 

 phores became a mass of ice. 5 As the temperature fell the 

 paddle plates continued beating without interruption. Ice 

 crystals formed about the ctenophores, finally enclosing them, 

 yet while half of an animal was solidly embedded in the advancing 

 ice the paddle plates of the free half continued beating as before. 

 Not until the impinging ice crystals actually imprisoned the 

 plates and held them fast did movement cease. 



Mayer ('14) emphasized the fact that whereas tropical marine 

 animals commonly live within 5 C. of their temperature of 

 maximum activity and within 10-15 C. of their upper death 

 temperatures, marine animals of the temperate or arctic regions 

 show but little change in activity within a considerable range of 

 temperatures. Hunter ('04) showed that Mnemiopsis leidyi is 

 relatively more resistant to a decrease than to an increase in 

 temperature of the water. The bearing of these observations 

 on the distribution of Mnemiopsis in New Jersey will be con- 

 sidered in the last section of this paper. 



IV. 

 THE FOOD HABITS OF CTENOPHORES. 



Little is known of the feeding and food habits of ctenophores. 

 Their delicate structure and relatively short life under laboratory 

 conditions, together with their somewhat sporadic appearance 

 within the reach of laboratories, have made investigation of their 

 habits difficult. Mayer (12) notes that "young Beroe CHCiimis" 

 devours Pleurobrachia "with avidity." Bigelow ('15) observed the 

 great impoverishment of the plankton on German Bank due to 

 Plenrobrachia pileiis, which "when it swarms seems to obliterate 

 or devour almost everything else in the water." Kincaid ('15) 



* Moore ('24) observed the beating of the paddle plates of Mnemiopsis at 0.6 

 C. under laboratory conditions. 



