788 SUMMARY OF CURRENT RESEARCHES RELATING TO 



c. The finer structure of the luminous organs. — The histology of 

 the two layers is next described. The appearance of the luminous 

 cells in their living and dead form, the occurrence of the yellowish- 

 green pigment, formed during the luminous process, the acid reaction 

 of the layer, the effect of various reagents, the relation of the tracheae 

 to the luminous organ, (fee, are intimately discussed. (2) The non- 

 luminous layer consists of tracheae and loosely packed irregular 

 masses, and is not definitely separable from the luminous stratum 

 above. The masses consist of urates, probably with potassium and 

 calcium bases. A well-developed layer of muscles, below the luminous 

 organ, doubtless serves to force the air from the larger tracheal stems 

 into the finer branches, and thus aids in the luminous process. 



d. Tlie phenomena of the luminous function. — Herr Heinemann 

 describes the phenomena of the luminous process both in the living 

 and dead beetle, noting the colour, intensity, and spectroscopic 

 relations, the variations under different circumstances of flight, sleep, 

 time of day, &c. He distinguishes the soft light seen on the sleeping 

 animal or on excised portions, from the blaze exhibited during active 

 respiration. His study of the relations of the organs to the respiratory 

 system leads him to explain the variations of light by reference to the 

 distribution, &c., of the tracheae. The light is brightest and lasts 

 longest in those portions which are nearest to tracheal branches of 

 considerable calibre. He shows that the tracheal system of the 

 posterior organ is quite independent of the thoracic, since inspira- 

 tion through the latter does not excite luminous function. Nor is 

 there any communication between the tracheae of the luminous organ 

 and those of the rest of the posterior portion of the body. By a 

 similar reference to the tracheal system, he explains the differences 

 between the luminous function of the Pyrophori and that of the 

 Lampyridae. In criticizing Max Schultze's emphasis on the role 

 played by the terminal tracheal cells, he notes— (1) that the luminous 

 organs of the Cucuyos are wholly destitute of tracheal terminal cells ; 

 (2) that the luminous cells are only browned and never blackened 

 by osmic acid, which does not harmonize with the connection between 

 luminosity and blackening by osmic acid, which M. Schultze sought 

 to demonstrate in regard to the Lampyridae ; (3) that the non- 

 luminous layer, on the other hand, behaves to osmic acid exactly as 

 the tracheal terminal cells of the Lampyridae, and (4) that the 

 " punctate " appearance of light, which Schultze explained by refer- 

 ing it to the tracheal terminal cells, is really explicable in terms of 

 tracheal distribution. The luminosity of excised portions, which 

 may in a damp chamber remain functional for two or three days, is 

 then discussed. 



e. The influence of the nervous system on the evolution of light. — 

 As the result of a number of crucial experiments effected by cutting 

 the nerves at various places, the author has demonstrated that the 

 luminous function of the ventral organ is exclusively influenced by 

 the respiratory movements, and therefore only indirectly excited 

 through the central nervous system. No excitation of the ventral 

 cord resulted in luminous function. There are no special luminous 



