LUMINOUS ORGANS AND LIGHT OF PHOLADES. 257 



nevertheless the triangular organs receive their vessels as do 

 the cords from the network of the capillaries of the internal 

 part of the mantle. Investigations made with the object of 

 discovering the nerves of these animals, assured me that from 

 the branchial or inferior ganglion two trunks are given off, 

 which afterwards constitute each two other little ganglions 

 from which emanate the ramifications destined for the inferior 

 portion of the mantle, as also others destined for the siphons ; 

 from each proceed very fine filaments which I have been able 

 to follow as far as the triangular organs and cords. 



Wishing now to speak of the structure of these organs, I 

 may observe that sections made in every direction and treated 

 by every different method of preparation, have led me to 

 remark that they are only elevations formed of the subcuti- 

 cular tissue of the derma, being on the surface covered by a 

 special epithelium. This epithelium constitutes the small 

 very superficial white coating of these organs, and this epithe- 

 lium is worthy of a special description, since it produces the 

 phosphorescent matter. 



The Pholades, as also the analogous molluscs, are covered 

 in their soft parts by an epithelium which is usually covered 

 with cilia on the surface of the foot, the gills, and on the interior 

 surface of the mantle, and of the siphons, and is cylindrical 

 with a special cuticle on the edge of the mantle and on the 

 external part of the siphons, which in the Pholades is also 

 furnished with special papillae. This epithelium does not 

 exactly follow the surface of the organs, but introduces itself 

 profoundly into the special furrows which resemble those which 

 surround the cerebral convolutions, so that the epithelial 

 surface is much larger than it at first appears, just as one also 

 observes with the intestinal epithelium of many animals which 

 have not enteric glands properly so called. The furrows which 

 we have already observed in the triangular organs and even 

 those seen across the cords have the same significations as 

 the furrows which we have just mentioned ; nevertheless, 

 they are deeper and easier to see on account of the form of 

 the organ. 



The triangular organs and the cords since they form part 

 of the interior portion of the mantle are then covered with 

 a ciliated epithelium of the same form and of the same 

 dimensions as that which covers the adjacent organs, but 

 the contour of these cells is quite special. At first the 

 nucleus of these cells presents a granular form, and these 

 granulations project from the surface. This peculiarity of 

 the nucleus extends usually over the whole contents of these 

 cells, which also appear granular, so that their contours get 



