PKCULIAII SECRETIONS. 365 



able manner, that when a few individuals are swimming in 

 company, they emit so much light, that in a dark night a 

 person might see to read by its aid. But considerable suspi- 

 cions may be entertained on this subject, whether the light 

 is emitted by the bodies of "fish, or by the number of mi- 

 nute parasitical animals which adhere to the surface of the 

 skin. It is well known, that when fish begin to putrefy, 

 they appear luminous ; but the light is occasioned, not by 

 the flesh of the animal, but by numerous animalcula, whose 

 growth the putrefaction has promoted. To such a cause 

 may be referred the light observed by WILLOUGHBY, in 

 the Sparus pagrus*. 



Among the Mollusca conchifera, the Pholades, accord- 

 ing to the observations REAUMUR, possess a licjuor which 

 is luminous ; and the same property is possessed by the 

 Pyrosoma of PEKON, inserted among the Mollusca tunicata. 

 The crustaceous animals exhibit several examples of lumi- 

 nous species, such as the Cancer pulex of LINN.EUS, and 

 the Cancer fulgens of Sir JOSEPH BANKS -f. The Myria- 

 poda exhibit this property in the species of the genus Seo- 

 lopendra. The Insecta furnish examples in many genera, 

 as Elater, Lampyris, and others. Among the Vermes, 

 the Neries noctiluca has been long known ; and, according 

 to BROGUIEKE, the common earthworm^. The genera 

 Medusa and Beroe among the Acephala; and the Penna- 

 tula and Sertularia among the Zoophyta, are all remarkable 

 examples. 



The luminous quality appears to reside in afluid substance 

 in the Pholas, Pennatula, Medusa and many other animals. 

 In a species of cancer observed by Captain TUCKEY, in the 



Historia Piscium, 312. f Phil. Trans. 1810, p. 2(51 Tab. xiv. f, t, ?. 

 Journ. d'Hist. Nat. ii. p. 2G7. 



