248 PHOSPHORESCENCE. 



Reaumur had rendered it much more probable that the 

 Pholas dactylus, Linn., was the shell the Roman naturalist 

 had in view, though we admit that his description will dis- 

 turb no conjecture. Pliny says, the phosphoric fluid is so 

 abundant in them that it shines about the mouths of those 

 who eat the Dactyli, shines on their hands, and even on their 

 clothes, from drops falling thereon.* Now Reaumur ascer- 

 tained that the Pholas secretes the fluid in sufficient copious- 

 ness to answer this account; and not from any particular 

 gland, for the whole body oozes with it. He removed the 

 animal from the shell, and on placing it in the dark, the 

 light appeared to emanate from every part of the surface ; 

 and on tearing it to pieces the internal parts were found to 

 be equally huninous. When dug out from its furrow, the 

 animal contains much water within the shell, and as it drops 

 out, the drops become luminous in their fall. After having 

 handled this Pholas, Reaumur, at first by accident, and then 

 of purpose, washed his fingers in a glass of water, which 

 then appeared in the dark as a vessel of milk would do in 

 the full light of noon. The light does not last long, and 

 ceases whenever the liquor dries ; but it can be revived by 

 moistening the body on which it has dried, though in a faint 

 degree. If the Pholas itself is dried, and moistened after a 

 lapse of four or five days, either with fresh or salt water, the 

 luminosity feebly reappears. Immersed in spirits of wine 

 its luminous property is at once destroyed ; and when placed 

 in sea-water, although they have remained long illuminated, 

 yet the light grew faint and fainter until it at length was 

 extinguished. Putrefaction also extinguishes the light; and 

 Reaumur suspects that the sensibility of the mollusk to 

 putridity is so great that it will not show its light when in 

 the vicinity of decaying individuals. Its bluish-white light, 

 in short, is the stronger as the animal is lively, fresh, and 

 supplied with its fluids ; and more powerful in summer, and 

 at the period of propagation, than at other times. j- The 

 Mytilus lithophagus (Lithodomus, Cuv.) would seem to pos- 

 sess the same remarkable properties, for Mr. Charles Ulysses 

 tells us, ' ' that in the Bay of Naples the fishermen place the 



* Hist. Nat. ix. 87. 



f Mem. de l'Acad. Roy. des Sc. 1723, p. 292, &c. Tiedemann's Comp. 

 Physiology, p. 260. Macartney in Phil. Trans. 1810, p. 280. The article 

 "Animal Luminousness," by Dr. Coldstream in Cyclop. Anat. and Phys. iii. 

 197. Forbes and Hanley, Brit. Mollusca, i. 107. Mr. Garner infers that 

 phosphorescence in the mollusca is someway dependent, or at least con- 

 comitant, on ciliary motions ; but the phenomena seem irreconcilable with 

 this opinion. — Charlesw. Mag. N. Hist. iii. 303. 



