LUMINOUS ORGANS AND LIGHT OF THE PHOLADES. 255 



siphoiiophora, or that the luminous secretion had its source 

 in the interior of special glandular organs. To resolve this 

 problem I only employed a slight jet of falling water which, 

 directed in the dark on the animal whose mantle and anterior 

 siphon had previously been opened, carried off the exuberant 

 part of the liquid and allowed me to see the luminous organs 

 of these molluscs. I found that after washing, the light was 

 seen to be fixed in definite places, such as, firstly, an arch 

 corresponding to the superior edge of the mantle which 

 reached to the middle near the valves; secondly, two small 

 triangular spots placed at the entrance of the anterior siphon ; 

 thirdly, two long parallel cords in the same siphon. I must 

 also observe that, if the current of water was stopped, all the 

 body of the animal became suffused with the luminous matter, 

 and, as before, entirely shining ; thus I discovered that there 

 exist special organs from which the luminous matter emanates, 

 which has the appearance of being secreted all over the sur- 

 face of the animal to observers who have not tried the washing 

 experiment, which appears to have been the case with those 

 who up to the present have observed the pholades. Having 

 examined a great number of the animals in question, 

 which were abundantly found in the Gulf of Baja, I never 

 happened to com.e across one that differed from another as 

 far as the disposition of the luminous organs is concerned. 

 By amputating the corresponding parts to these organs, 

 all the luminous power of the pholades is extinguished. 



All these things discovered, it became necessary to know 

 what corresponds to the places from whence the luminous 

 matter springs. On the superior edge of the mantle there 

 is no organ at first seen, but, on the contrary, to the parts 

 above mentioned circumscript organs correspond, and I can- 

 not understand how they have escaped the observations 

 of naturalists who have occupied themselves with describing 

 the parts and structure of molluscs. Only in Poli, who 

 nevertheless made no special investigations on the light of 

 ])holades, do I find mention of these parts, what we have 

 called triangular organs and cords, without his having guessed 

 at all their attributes. " Quinam vero sit eorum usus pro- 

 muntiare non audemus." 



The place of the triangular organs and the cords once 

 ascertained, and wishing to examine them closely, one per- 

 ceives that these organs are a part of the mantle on which 

 they stand out in relief, whilst their whiteness contrasts with 

 the gray colour of the animal. The triangular organs present 

 parallel furrows running all through them, which separate 

 in all from five to twelve lobes, and the cords of the siphon 



