254 PROFESSOR PANCERI. 



which was the same as renders the Penatules luminous. 

 Without denying that there may be found marine animals 

 which, the same as the terrestial glow-worms, shine by the 

 slow combustion of an albuminous substance, or for some 

 other reason, it is, nevertheless, certain that some of the phos- 

 phoric animals of the sea owe their phosphoric properties to 

 a special matter which presents all the characters of a phos- 

 phoric grease, as Avell as the peculiarity of becoming luminous 

 in soft water, as in the other cases mentioned in this memoir. 



The Luminous Organs and the Light of the Pholades. 

 By Professor Paul Panceri. 



In continuation of the studies already made on luminous 

 animals, I now present to the academy a work on pholades, 

 concerning particularly the most ordinary species of our seas, 

 namely, the Pholas dactylus L. The phosphorescent pro- 

 perties of these molluscs has been for some time known, 

 and the luminous clouds which they spread in water when 

 touched or moved. Pliny describes this phenomena in 

 a special paragraph of his ninth book.^ His observations 

 were afterwards confirmed by many authors, and Reaumur 

 also wrote on this matter,^ expressing the belief that the 

 outer surface of the pholad creates this luminous matter, 

 illuminating the object it touches, and the water in which 

 one washes one's hands. According to Reaumur this same 

 matter if dried shines again when wet. Monti, Beccari, and 

 Galeati, as also their contemporary, Reaumur, were much 

 occupied on the subject, and made observations which 

 scarcely differ one from another. They maintain that pho- 

 lades shine most when in milk. The authors whom I cite in 

 my memoir confine themselves to describing the phenomenon 

 without indicating its precise situation. 



I myself once perceived the fact of the luminous clouds in 

 the water with pholades in it when shaking and troubling it, 

 and I also have seen their bodies luminous after opening the 

 mantle and the valves ; this is caused by an abundant liquid 

 which communicates light to the body it touches. I then 

 thought, since we have here to deal with a secretion, that 

 two cases might present themselves, either that all the surface 

 of the pholad and in all probability its exterior epithelium 

 might be the seat, as I have seen in the medusae and the 

 ' ' Histor. Mundi.' 2 ' Memoir de I'Academie de Science.' 



