46 MEMOIR III. 



seem to have no other use, unless we suppose them to be 

 given for the purpose of locomotion. For a confirmation of 

 this circumstance we naturally look to those Naturalists 

 who may find themselves favorably placed, to make obser- 

 vations upon living Pyrosomse. 



The other kind of luminosity of a more local nature, (E.) is 

 that which presented itself to the observation of Captain 

 Horsburgh, a gentleman richly entitled to National Honours 

 andtothe gratitude of posterity, for his valuable contributions 

 towardsthe safe navigation of a large portion of the trackless 

 Ocean. His example in the present instance deserves to be 

 imitated. At sunrise on April 12, 1798 in the Arabian Sea, 

 he perceived several luminous spots in the water, which 

 conceiving to be animals, he ivent in the boat, and caught 

 one : it proved to be an insect somewhat resembling in 

 appearance the wood-louse, (Oniscus) and was about one 

 third of an inch in length. When viewed with a micros- 

 cope it seemed to be formed by sections of a thin cutane- 

 ous substance. — "During the time that any fluid remained 

 in the animal it shone brilliantly like the fire-fly." Taken 

 from his notes given to Sir Jos. Banks, as quoted by Prof. 

 Macartney, Phil. Trans. 1810. who has appended to his 

 paper, PI. XV. f. 4, an engraving of the animal copied after 

 a pen-sketch by Captain Horsburgh. Having had the good 

 fortune to meet with this same animal (PI. 8. f. 2. a. b. c.) 

 by day light while in soundings near to the Belliqueux 

 Shoal, which lies off^ the South extreme of the island of 

 Madagascar, and again on the Agullas Bank near to the 

 Cape of Good Hope, August 9th, 1816, I am entitled to 

 say that it is no Limulus as suggested by the learned Pro- 

 fessor, and although not sufficiently scrutinized by me to 

 determine its actual structure, is an animal which it is 

 impossible to associate with any other genus of the Crus- 

 tacea. Individually I feel under great obligations to this 

 beautiful little animal, which by its splendid appearance 

 in the water induced me to commence the use of a muslin 



