TUNICARIES. 227 



animals, the Atlantic species 1 being about five 

 inches long, and the Mediterranean* sometimes 

 attaining to the length of fourteen. Their power 

 of emitting light is so great that in the night 

 they cause the sea to appear on fire. Nothing 

 can exceed the dazzling light and brilliant 

 colours that these floating bodies exhibit co- 

 lours varying in a way truly admirable, passing 

 rapidly every instant, from a dazzling red to 

 saffron, to orange, to green, and azure, and thus 

 reflecting every ray into which the prism divides 

 the light, or which is exhibited by the heavenly 

 bow. In the water their position is generally 

 horizontal, and their locomotion very simple : 

 they float, as they are carried by the waves or 

 the currents ; like the salpes, they can however 

 contract and restore themselves individually, and 

 have also a very slight general movement which 

 causes the water to enter their common cavity, 

 visit their gills for respiration, and convey to 

 them the substances which constitute their food. 

 M. Le Sueur observed that when the central ca- 

 vity of the common tube was filled with water, it 

 was immediately spirted forth in little jets from all 

 the extremities of the tubercles with which the 

 surface was covered, from whence it appears that 

 the external aperture of the individual animal 

 is really the anal aperture, and the opposite 

 or internal one the mouth, which thus received 



1 P. atlanticum. 2 P. giganteum. PL. IV. FIG. 3. 



