[36] PAGE 44. _Dendronotus arborescens._ A curiously decorated marine slug, found on the algæ 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 Professor 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 glow-worm 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 it, I got a favorable magnifying power, A of Zeiss. With stronger objective there is no good effect. “The eye is at first dazzled by a strong, uniform yellowish light. But the intensity of this light is soon checked, the luminous field being interrupted by round spots. The light continues to diminish; the image becomes paler; and between the obscure round spots are seen to appear confused shadows, which detach themselves from the more brilliant rings. These rings are last to disappear when all the other portions have become dark. In the end they disappear entirely. “The organ remains dark until the next flash; only here and there brilliant isolated points persist, which, as we shall see later, represent parenchymal cells which have retained their activity. If one places under the microscope the detached abdomen of a normal Luciola, and excites it by pressure of short duration by the cover glass, it is possible to obtain a flash which resembles the physiological flash.” M. Emery states that he found it unsatisfactory to examine the insect while alive, as the constant movements rendered it nearly impossible to observe correctly the phenomenon of luminosity. He proceeds: “I have found by poisoning the Luciola by vapors of osmic acid an excellent method in fixing the light, and studying exactly the microscopic aspect.