PECULIAR 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 hght 
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 ight observed by WuittovucHsy, in 
the Sparus pagrus*. 
Among the Mollusca conchifera, the Pholades, accord- 
ing to the observations Reaumor, possess a liquor which 
is luminous; and the same property is possessed by the 
Pyrosoma of PEron, inserted among the Mollusca tunicata. 
The crustaceous animals exhibit several examples of lumi- 
nous species, such as the Cancer pulex of Linnxus, and 
the Cancer fulgens of Sir Joseph Banks. The Myria- 
poda exhibit this property in the species of the genus Sco- 
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 Brucuirrre, 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 chserved by Captain Tuckey, in the 

* Historia Piscium, 312. + Phil. Trans. 1810, p, 262. Tab. xiv. f. 1, 9, 
; Journ. dHist. Nat, ii. p. 267. 
