164 LECTUEES ON BIOLOGY 



our glow-worm are frequently worn by ladies as living ornaments 

 in the hair, or enclosed in little medallions, as brooches, for 

 their brilliant sparkle vies with the costliest diamonds. 



Glow-worms possess phosphorescence for purposes of repro- 

 duction, for it helps the sexes to find each other. In other 

 animals it may serve to attract the prey or to deter enemies; 

 but there are also numerous other organisms to which it gives no 

 demonstrable advantage. 



The most magnificent instance of organic light-production is 

 observed on the ocean. Never shall I forget the wonderful im- 

 pression which I received when noticing for the first time this 

 wonderful spectacle on the Algerian coast. A mild spring even- 

 ing had kept us on the sea till darkness. When at last we were 

 making for the shore there rose every now and again, here and 

 there, sparks giving a bluish light. Gradually the phosphor- 

 escence became more and more frequent and intensive, each wave 

 bursting into a rain of fire. On our bow silver drops glittered 

 and glistened, and each stroke of the oars called forth myriads 

 of lights. It was a veritable fairyland of light and splendour. 

 The magicians which performed this miracle were little uni- 

 cellular organisms belonging to the Infusorians. Their names 

 are Noctiluca and Leptodiscus. They are barely 1 millimetre in 

 diameter, and their organization can only be observed with a 

 microscope. If we examine them we see that specific luminous 

 organs are absent, and that it is the whole cell-body which lights 

 up at the slightest stimulus of a mechanical or chemical nature- 

 Of their mode of life only very little can be said : they float on the 

 surface of the water, drifting with the current ; if storms, rain, 

 or cold approach they sink down to a depth where there is eternal 

 calm. Only during favourable weather they rise to the surface, 

 often in such vast swarms that during the day the sea for 

 long distances appears to be covered as with a reddish film. 

 The rising and sinking of the Infusorians in the water is 

 probably effected by taking in and ejecting sea water, a process 

 by means of which they alter their specific gravity. The little 

 creatures do not appear to derive any advantage from their 

 phosphorescence. 



If different instances of colour-adaptation showed us many 

 strange things, the phenomena of mimicry cause still greater 



