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JOURNAL, E.A.S. (CEYLON). [Vol. IX. 



was, that, as is known to be the case with insects, every 

 spine is provided with a peculiar bag of poison, the spine 

 itself being hollow, and the poison flowing out of the bag 

 through it into the wound; the blue corpuscles especially 

 have round the bag of poison a fairly thick ball of muscular 

 substance, and this contracts if the fine spine inside of the 

 corpuscle penetrates into the skin. We have no doubt that 

 a similar apparatus also exists in the other leather-urchins, 

 but it has not yet been determined. It is evident that this 

 soft sea-urchin would soon be destroyed by fishes of prey if 

 it had not the formidable arms just described. This circum- 

 stance a small fish availed itself of ; this little animal, 

 which is in length about one inch, lived just between the 

 spines of the sea-urchin, so that a pursuing fish could not 

 come near it at all without being wounded by the spines 

 of the sea-urchin ; moreover, the little fish had the same 

 dark brown colour as the sea-urchin, and was thus doubly 

 protected. 



Until now in no sea-urchin had a real eye been found. It 

 was noticed that many had a very feeble perception of 

 light ; but it was impossible to state that they could really see. 

 This is quite correct of the great majority of the sea- 

 urchins ; but in the geuns Diadema, which is very common 

 throughout the tropics, we found most curiously composed 

 eyes, somewhat similar to those of insects. As light blue 

 spots they run round the surface of the black sea-urchin, 

 like the above described blue corpuscles of the leather- 

 urchin. Each of these blue spots consists of many hundred 

 small crystal cones, which rest upon a layer of nervous 

 substance. Microscopical examination had already shown 

 that the blue spots were eyes, and the simplest physiological 

 experiment confirmed it. If the hand is brought near the 

 aquarium which contains the sea-urchin, without touching 

 the water of course, the urchin at once directs all its long 

 spines against it to protect itself ; it sees therefore very well. 

 Between the spines of Diadema a little fish lives, which 



