174 APPENDIX. 



is covered with ciliated epithelium, which dips down into all the parts 

 of the animal; but the special epithelium differs from this. It is 

 nucleated and crammed with granules, and the cells are very refractive. 

 The cells are very fragile, and allow their contents i.e., granular nuclei 

 and refractive granules to escape readily. These are soluble in ether 

 and alcohol. Under ordinary circumstances this photogenic apparatus 

 is hidden ; but violence readily displaces the special cells, which burst, 

 and their contents are carried all over the surface by the water, assisted 

 by the general ciliation. The white substance, fat-like, retains its 

 luminosity, when spread out on paper, for hours ; but the light does not 

 appear to be accompanied by an evolution of heat. When it is placed 

 in carbonic acid gas, the light pales and ceases. On the other hand, 

 the photogenic substance, when barely luminous, is rendered so by 

 physical contact. Agitation, and the addition of fresh or salt water, 

 develop the light, and the same effect is produced by electricity and by 

 heat. The light is monochromatic, and has a constant place in the spec- 

 trum as an azure band from E to F, that is to say, in the green." 



36. PAGE 44. Dendronotus arborescens. A curiously decorated marine 

 slug, found on the algse of the waters around Massachusetts Bay. Eolis 

 is another form nearly as interesting. 



37. PAGE 55. The spectrum of the light of comparatively few of 

 these beetles has been examined. That of Photinus was found by Pro- 

 fessor C. A. Young, the astronomer, to be continuous without lines, and 

 to extend from Fraunhofer's line C in the scarlet, to about F in the 

 blue. 



Mr. Meldola examined the spectrum of the light of the glowworm 

 some years ago, and found that it was continuous, being rich in blue and 

 green rays, and comparatively poor in red and yellow. 



38. PAGE 56. Professor Carl Emery of the Entomological Society of 

 Italy has kindly sent to us a detailed account of his experiments with the 

 illuminating apparatus of a native luminous insect, the Luciola italica, etc. 

 As these are the latest conclusions by the highest scientific authority, 

 and therefore to be regarded as the most reliable, we here present a full 

 account. 



" The elytra of the insect Luciola were glued upon a holder of the 

 microscope, and covered by a glass of tolerable thickness. On examining 



