44 MEMOIR III. 



surface, belonging to the class of Tunicata, and first disco- 

 vered and figured by Messrs. Peron and Le Sueur, (Voyage 

 aux Terr esAustr ales, ^om. I, p. 448, pi. 30, fig. \.m\^Annales 

 de Museum, torn. 4, p. 440. A figure of it may be seen in 

 Shaw's Zoological Lectures, plate 127- The light which 

 this animal yields, appears to pervade its whole substance, 

 and when examined near at hand, varies in intensity and 

 in shade, often exhibiting a very beautiful phosphorescence 

 of a blueish or greenish tinge, like a pale sapphire or 

 aquamarine as it gradually fades away ; agitation or fric- 

 tion renews it as in other luminous animals as long as it 

 continues to exhibit signs of life, but it is most vivid, when 

 the animal is first drawn up, and at length can scarcely be 

 called forth by the rudest treatment. As we observed this 

 interesting animal, with Milbert's florid description at 

 hand (Voyage Pitt or esque a VIsle de France, torn. I. p. 110.) 

 I can aver, that the red, aurora, and orange colours, did 

 not present themselves to the eyes of any of our numerous 

 party, who were nevertheless, highly gratified at the sight 

 of so brilliant and singular a creature. 



This plicnomenon may often be witnessed by vessels 

 bound to India or the eastward of the Cape of Good 

 Hope, occurring in the calm latitudes near to the Line. 

 Peron's observations led them to restrict the limits of its 

 habitation between the 19° and 20° of Long. W. of Paris, 

 and the 3° and 4° of N. Lat. We first fell in with the Pyro- 

 soma however, in N. Lat. 12^ and carried it Avith us all 

 the way to the Line, between the Longitudes of 16° and 

 20° W. Ships generally cross the Equator to the West- 

 ward of W. Long. 20° to avoid the calms which prevail 

 nearer to the African coast, those therefore, which from 

 necessity or choice pass to the eastward of this longitude, 

 may expect to meet with the Pyrosoma, within the limits 

 indicated above. As we approached the Equator, a smaller 

 species made its appearance, intermingled with the former ; 

 in this, the luminosity is more condensed about the mouths 



