332 KUPERT VALLENTIN AND J. T. CUNNINGHAM. 



as on their ventral surface when swimming, or perhaps oftener 

 in the latter position. This is of some importance in relation 

 to the ventral position of the luminous organs. The contrast 

 between the apparently excited, hurried, heedless motions of 

 Nyctiphanes, and the graceful, wavy movement of Mysis, 

 which is always either suspended in perfect balance with a 

 regular motion of its limbs, or escaping by a swift, well- 

 directed, backward dart, is very striking. 



In total darkness the animals swimming about in a glass jar 

 of sea-water gave out short flashes of light from time to time. 

 Each flash was of short duration, but sometimes lasted longer 

 than at others ; when several animals gave out light simul- 

 taneously or in rapid succession, the effect was very brilliant 

 and beautiful, but nothing like continuous luminosity was ever 

 observed. 



Handling. — When the hand was plunged in the water 

 among the animals, any one of them when touched immediately 

 gave forth a flash. When an animal was caught and removed 

 from the water between the finger and thumb, all the organs 

 emitted a brilliant light for five to ten seconds, while the 

 creature was flapping its abdomen vigorously and trying to 

 escape. Then followed an interrupted series of flashes lasting 

 ten seconds more, and then the animal would become quiet and 

 no light could be seen. But when slight pressure was adminis- 

 tered, all the organs flashed again, the duration of the flash 

 being longer when the pinch was stronger. When the animal 

 was crushed between the fingers and the tissues rubbed 

 between the hands, certain particles were luminous and re- 

 mained continuously so until they were dry. When an 

 organ was dissected out from the abdomen the light ceased, 

 and by the time it was mounted and placed under the micro- 

 scope all luminosity had vanished. But when the organ under 

 the microscope was crushed the field was lit up and continued 

 so for some time. When an eye-stalk was cut off by scissors 

 the ocular organ became luminous for an instant when the 

 division took place. After the animals had been in captivity 

 twenty-four hours, they were by no means so easily excited to 



