258 PROFESSOR PANCERI. 



mixed, and it is not always easy to define them. These 

 cells, far from resembling those of the ciliated epitheliums of 

 the other parts, are fragile and easily allow their contents to 

 escape. It is sufficient to touch with a glass slip the surface 

 of one of these organs that has never before been touched, to 

 see immediately a white matter attach, which shines and 

 which under sufficient magnifying poAver is seen to be com- 

 posed of granular nuclei, of very fine granulations, of small 

 greasy drops, and even of granular masses which represent 

 the entire contents of the cells of which they preserve the 

 form. A fold of the epithelium of the same nature is that 

 which renders luminous a band placed under the superior 

 edge of the mantle ; it is thus that is obtained the luminous 

 arch before mentioned. 



After having compared this epithelium with that of the 

 phosporescent medusae, and having pointed out the difference 

 vhich exists as to the disposition and the form of the matter 

 it contains, the phosphorescent organs are compared to those 

 of Pyrosoma. In so far as that in these also the luminous 

 organs are formed of cells which belong to the exterior 

 coating. Nevertheless in the Pyrosoma these organs are very 

 deep and their elements fixed, while in the pholades they 

 are formed of elements placed on special and fragile out- 

 growths so that their product, as happens in a secretion, 

 can be poured out externally. 



The luminous matter contained in the cells of the lumi- 

 nous epithelium is soluble in alcohol and ether ; audit would 

 be very important for chemists to study it closely, so much 

 the more so as it is easy to procure it where Pholades are 

 abundant. 



The second part of my work contains the results of experi- 

 ments made on the entire animal and on the isolated luminous 

 matter, and I also take note of the energetic action of soft' 

 distilled water employed both at 0° and at a very much 

 higher temperature, as also the action of alcohol and ether 

 which have the power of evoking the light, and in a few 

 minutes extinguish it. 'I he luminous matter was spread on a 

 sheet of paper and then placed first in pure oxygen, and then 

 in carbonic acid ; neither in the first case did it shine more, 

 nor in the second did it become extinguished, but remained 

 the same, that is to say, it ceased little by little. This question 

 has been treated by me in my work on the Pennatulse. If 

 the Pholades are exposed in air or in oxygen the light will 

 continue for three or four days, or even more ; while in car- 

 bonic acid, it becomes extinct in one hour, but if after its 

 extinction one exposes it again to the open air the light 



