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raal, are a sort of small fins or wings, which seems to be 

 the instruments of its motion. It has two small horns 

 issuing from the fore part of its head, and its tail is cleft 

 in two. Their whole body is luminous, and when cut to 

 pieces, every piece emits a vivid light for some time ; 

 probably so long as the conclusive motion of the dying 

 parts continues. 



Many philosophers of the first rank have imagined that 

 tlie luminousness of the sea water in the night season js 

 occasioned by some electric matter. " The surface of i he 

 sea," say they, " having been exposed all the summer to 

 the impulse of the solar rays, when it begins to be agi- 

 tated by the autumnal winds, throws out luminous sparks 

 perfectly similar to those which issue from electrified 

 bodies/' 



But occular demonstration now convinces us, that this 

 brightness is frequently, if not always, to be ascribed to 

 the little animals. 



The light of a glow-worm is so strong, that it will 

 shew itself through several substances. The creature 

 seems dead in the day time, and its light is not then vi- 

 sible even in a dark room, unless it be put in motion, 

 and then it is very faint. After sun-set .the light begins 

 to return, and with it thejjfe and motion of the animal. 

 Indeed, the motion and light seem to depend on each 

 other ; it never shines, but when it moves : and when it 

 shines most, the body is one third longer than in the day 

 time. While it shines brightest, it sometimes turns 

 about, and the light is no larger than a pin's head. But 

 on being touched, it immediately extends itself, and the 

 light is as large and bright as ever. 



The luminous parts are two small specks tinder th6 

 tail. The use of its light is, to direct the animal in its 

 course, and in taking of its prey. It is admirably placed 

 for this purpose. The tail is easily bent under its belly, 

 and throws its light full upon any object, about or under 

 the head of the animal, and the eyes are placed not on 

 the upper part, but on the under side of the head, s6 

 I 2 



