LUMINOUS ORGANS AND LIGHT OF THE PHOLADES. 259 



reapjiears. It is worthy of special mention that the luminous 

 light of the Pholades in heated sea Avater lasts until 73°C., and 

 sometimes attains 76° C. The action of electricity is not 

 very powerful, and the effect of solar light in no way 

 modifies the luminous power of the Pholades. Numerous 

 experiments prove the great analogy of the phosphorescent 

 matter of these molluscs with that of the animals we have 

 already studied. 



In the analysis of this light I find the spectroscope of 

 Sorby and Browning applied to the microscope, which Mr. 

 Kay Lankester had the kindness to offer me, useful beyond 

 all others. This spectroscope, allowing two rays to pasis 

 through the same prism, has the advantage of having two 

 contiguous spectra, one of the solar light, the other of the 

 substance under examination. Having used gas light on 

 this occasion it was necessary to make this light pass through 

 a substance which would furnish lines of absorption of 

 which the place was already known in respect to the solar 

 lines. The substance used in this case was the solution 

 of permanganate of potash, which gives five distinct lines. 

 Things being thus arranged, we submitted to observation 

 the triangular organs and the cords, employing ether to 

 excite them. The light Avas very vivid for some minutes, 

 so that one had full time to examine them. The light 

 of the Pholades is monochromatic like that of the Beroes, 

 of the Alcynoes, of the Ippopodiunis, of the Medusae, of 

 the Eledones already observed. However, the azure band has 

 a permanent place, and extends from line E to line F, passing 

 the former by very little. It would be very important to 

 observe if the band of light of other marine animals that are 

 also monochromatic is found in the same place. 



We will now give the entire conclusions this memoir 

 arrives at ; they are — 



1. That in the Pholas dactylus are found special organs 

 which give out light in certain particular cases, and which 

 produce a luminous matter, which appears to be a secretion. 



2. The organs are formed principally of ciliated epithelium, 

 containing in its cells the special granular substance which 

 renders the water luminous, and which mixes with the mucus 

 which separates from the surface of the animal ; this matter 

 is soluble in alcohol and ether. 



3. This epithelium in the above-mentioned species is found 

 under the superior edge of the mantle, and in those organs 

 which we have called triangular organs and cords. 



4. The luminovis matter of the phosphorescent epithelium 

 escapes from these organs when the animal is submitted to 



VOL. XII. NEW SER. T 



