Specific Gravity and Luminescence in Noctiluca, etc. 245 



CENTRIFUGING. 



On centrifuging noctilucas for 3 to 5 minutes with a hand centrifuge, 

 the animals form a layer at the surface of the liquid, and in each animal 

 the protoplasm is thrown to the bottom of the cell as the heaviest 

 material. The animals do not orient themselves in any way in the 

 centrifuge, but the protoplasm is thrown to whatever part of the cell 

 happens to be toward the centrifugal pole. After about an hour, many 

 of the animals recover, and the protoplasm may be seen under the 

 microscope returning to its normal position near the mouth-groove and 

 flowing along protoplasmic strands to the periphery of the cell. No 

 separation of the materials of the protoplasm into layers was observed 

 with the centrifugal force used. The effect of centrifuging upon the 

 luminescence is practically nil, for the animals give a normal response 

 as soon as taken from the centrifuge tubes and placed in a dish of sea- 

 water. 



ELECTRICITY. 



When a constant current is passed through a mass of noctilucas, 

 the animals flash brightly at the make, continue glowing during the 

 passage of the current, and cease to glow at the break, giving no flash, 

 but sometimes they stay glowing after the break, and in this case the 

 stronger the current the longer the glow lasts. If stimulated mechani- 

 cally while the current is passing, they respond by a flash, just as 

 when no current is passing. 



The light comes from all parts of the noctiluca and is not restricted 

 to anode or cathode regions. No increase in luminosity could be 

 observed on the cathode side nor decrease on the anode side of the 

 animal comparable with the polar effects of the current on muscle. 



The tentacle movement is also influenced by the passage of a con- 

 stant current. At the make, the tentacle coils up rather tightly, like 

 a watch-spring, and at the break it uncoils, the process being repeated 

 for a number of makes and breaks. This tentacle response is similar to 

 the abnormal behavior of the sartorius muscle of a frog, which some- 

 tunes contracts on the make, stays contracted while the current is 

 passing, and relaxes on the break. Spaeth (1916) similarly found that 

 the pigment cells of fish-scales contract on the make, stay contracted 

 during the passage, and relax on the break. 



When a mass of noctilucas is subjected to the induced currents of 

 an induction coil they respond with a flash at the break, and at the 

 make also, if the current is strong enough. 



If subjected to an interrupted induced current for 45 seconds, the 

 animals flash on the first shock and then remain glowing, but the 

 luminosity becomes gradually fainter. If the current is now stopped 

 for a moment and then passed again, there is again a bright glow. 

 The animals therefore fatigue rather readily when stimulated electri- 

 cally, as they also do with mechanical stimulation. 



