312 



THE AMEBIC AX NATURALIST 



[Vol. XLY 



Joseph H. Kastle, of the University of Virginia, is of 

 especial interest in this connection (6). 



Our histologic methods presented no particularly new 

 features. Most of our specimens were killed in hot 70 

 per cent, alcohol, stained entire in acid carmine, and 

 mounted in paraffin. To secure proper penetration of 

 the stain, it was found necessary to clip off the tip of the 

 abdomen, or to slit the dorsal chitin. Osmic acid prepa- 

 rations were used a number of times, and in the sections 

 of Phot inns consanf/uinrus, which were otherwise un- 

 satisfactory, one per cent, osmic acid gave very good 

 results for the fine tracheolar structure. For the study 

 of the tissues under the dissecting microscope a good 

 treatment was found to be to allow the detached, fresh 

 luminous segments to soak in a mixture of equal parts of 

 ten per cent, caustic soda and ten per cent, formaldehyde 

 solution for three or four hours. This treatment left 

 the tissues of both the reflecting and the active layers of 

 the same gross appearance, though without entirely de- 

 stroying the cellular structure; after being treated thus, 

 the trachea' and tracheoles can be seen as silvery white 

 tubes and threads, on a background of dull, pale yellow, 

 and may be followed down to the point of anastomosis. 



It seems possible that the reflecting layer fulfils' a two- 

 fold purpose— that of reflecting the light outward, and 

 thus increasing its intensity in the desired direction, and 

 of protecting the insect itself from its own radiations. 

 It has recently been shown by Coblentz (7) that the 

 pyralis and other Lampyridse contain a fluorescent ma- 

 terial, and a number of observers have shown that 

 fluorescent materials injected into a living animal show 

 a higher degree of toxicity when the animal subsequently 

 is exposed to light than if it be left in the dark. 



To conclude: We have found that (a) the structure of 

 the photogenic organs in Photinus pyralis, Photinus 

 consfuirjituteus and Plwturis pcnnsiflnnnca is practi- 

 cally the same, and very similar to the structures of the 

 corresponding organs in some of the other species of 

 Lampyridae that have been studied; (b) the trachea? from 



