PHOSPHORESCENCE. 



249 



A portion of a chain of small 

 Dagysre of the natural size, and 

 considerably magnified, to show 

 the course of the intestine : a, 

 the mouth ; b, the anus. (From 

 Home's Lect. on Comp. Anat. 

 vol. ii. t. 73). 



animal in the sun, and with it besmear their hands and faces 

 at night, so as to illuminate them as with phosphorus."* 

 The two genera have the same habits, lying concealed in 

 deep holes which they have bored in clay and rocks, and for 

 what purpose they light up their gloomy cells, unless it be 

 to allure some minute insect i)rey, it is hard to guess, for 

 they themselves are " dark in light." 



It is, however, p. ^^ 



among the Tu- '^" 



nicata that the 

 most consider- 

 able phosphores- 

 cent species are 

 found. The no- 

 mad tribes of this 

 order abound in 

 tropical seas ; 

 and there are few 

 of them that do 

 not light up their 

 lamps in the 

 dusk. The Sal- 

 pae (or Dagysae 

 of Banks, Fig. 

 43,) linked to- 

 gether in living 

 chains, and the 

 Pyrosomae, are 

 the most remark- 

 able examples. Both genera appear to emit the phosphoric 

 flame only when the water is agitated, or when they come in 

 contact with opposing bodies, or when they rise above the 

 surface of the water. In his observations on a species of 

 Salpa, Mr. Beaufort informs us that it gave no light unless the 

 water was violently agitated. "On holding one in my hand," 

 he adds, " and gently pressing it, a faint flame seemed to per- 

 vade the w4iole inside ; and on each projecting point there 

 seemed to stand a little globule of very vivid light. On 

 increasing the pressure, its brilliancy likewise increased for a 

 few moments, then gradually declined for some time, as if 

 exhausted by the exertion. It may have been fancy, but, 

 at the time, I was convinced that it gave out a sensible 

 degree of warmth to the hand."f The latter observation is 



* Dillw yn's Cat. Rcc. Shells, p. 303. 

 t Home's Lectures, i. 367. — This seems very positive evidence, yet Forbes 



