186 M. de Quatrefages on the Phosphorescence of 



in diameter, in which the NoctiluccB formed a bed at the surface 

 nearly 20 miUims. thick, the figures of a watch face could be read ; 

 but strong agitation of the tube was necessary, and it was requi- 

 site to hold it close to the glass of the watch. Four to five tea- 

 spoonsfull of Noctilucce were collected in a filter, and on pro- 

 ducing the phosphorescence by this means the houi' could be 

 told at the distance of a foot. 



5. No disengagement of heat sensible to a thermometer accom- 

 panies the phosphorescence. — This fact was established by placing 

 the bulb of a thermometer in the Noctiluca water while it was 

 quiet, and then giving it a shake to produce the phosphorescence. 

 The experiment was varied in diifereut ways. 



6. The light of the Noctilucse may he produced over the whole 

 surface of its body or only a part of it. — After a violent agitation, 

 the Noctilucce retain the phosphorescence for some time, so that 

 it may be studied at leisure. With a lens magnifying 6 to 8 dia- 

 meters, it is easy to see that while some of the Noctilucce are 

 phosphorescent throughout, others are but partially so. In the 

 figure PI. A^I. (fig. 7), one of the animals is light over its whole 

 surface, and the other (fig. 8) only on opposite sides. "With a lens 

 of 10 to 12 diameters we find that the light often appears success- 

 ively on diff'erent parts of the body. There is hence no circum- 

 scribed phosphorescent organ, as in the Lampyri, Elaters, and 

 Pyrosomas*. 



7. The light is due to an infinite number of minute scintilla- 

 tions. — Figui-e 9 of a part of a Noctiluca much magnified, re- 

 presents the actual character of the phosphorescence. There 

 is an immense number of points of fight. With a lens of 

 20 to 30 diameters, the light is like an undefined nebula ; but 

 with a lens of 60 diameters it is partially resolved, and with 

 150 diameters, wholly, into its constituent spangles. Each lumi- 

 nous spot on the body is found to consist of a cluster of minute 

 instantaneous scintillations, dense at the centre, and more scat- 

 tered towards the circumference of the spot. Thus the same 

 phsenomena take place in the Noctilucce as were obsei-ved by 

 M. de Quatrefages in the Ophiurce and Annelida. Each spot 

 of light is resolvable into constituent points, and consists of 

 evanescent scintillations. 



* The Noctiluca (PI. VI. fig. 6) has a depression on one side, and near the 

 middle of this depression is the mouth. At the same place there is a move- 

 able appendage as long as half the diameter of the animal. The body is 

 perfectly transparent. The general envelope consists of two membranes 

 distinguished with difficulty. The outer is excessively thin and like an 

 epidermis ; the inner is thicker, but without a trace of fibres. On com- 

 pression the envelope acts like a bag full of liquid, and finally bursts. 

 Numerous anastomosing and branching lines radiate from the mouth 

 through the granulous interior. 



