596 SUMMARY OF CURRENT RESEARCHES RELATING TO 



themselves to physiological analysis ; they are found hetween 30° S. 

 and 30° N. of latitudo, and between 40° and 180° of longitude. 

 The emission of light is intimately connected with the accom- 

 plishment of an important physiological function, but in some raro 

 cases there is no luminosity. The position, form, and powers of the 

 luminous organs vary slightly in different species, and a few have no 

 such organs. One of tho most brilliant is Pyrophorus nodilucm, which 

 has been especially studied by M. Dubois. In the necessary pre- 

 liminary anatomical study certain corrections were found to be 

 necessary with regard to tho situation of tho stigmata, tho distribu- 

 tion of the trachea), and the relations of the nervous system to the 

 light-producing organs. 



Tho organs themselves are composed of a special adipose tissue 

 and of certain accessory organs ; histochemical investigation revealed 

 the presence of a body which presents the characters of guanin. 

 Intcuse histolysis takes place within the photogenous adipose tissue, 

 the changes being provoked or stimulated by the penetration of blood 

 into the luminous organ ; this histolytic process is accompanied by 

 the formation, within the photogenic cell, of a vast number of small 

 crystalline agglomerations of special optic properties, and especially 

 remarkable for their double refraction. 



The presence of blood is not, however, indispensable for tho 

 production of light, for the ovum is luminous, even before segmenta- 

 tion, and the adipose photogenic cell, when isolated, exhibits the 

 same property; these facts point to a similarity between the sub- 

 stance of the adipose body and that of the vitellus. The larvae, 

 which, hitherto unknown, have been by the author found to resemble 

 those of other Elateridre, are luminous; at first they have but a 

 single luminous organ, but this extends over all the segments, and is 

 localized at the points where histolysis is most active. In the adult 

 insect there are three luminous spots which are so placed as to aid 

 walking, swimming, and flying in obscurity. The muscles of the 

 luminous organs regulate the supply of blood to the photogenic 

 organs, and so have an indirect action on the production of light ; 

 the nerves act through the muscles ; the photosensitive reflex action 

 has its seat in the cerebroid ganglia ; centrifugal irritation of tho 

 ganglia produces the appearance of the light, but this is not the case 

 with centripetal stimulation. Respiration has only an indirect 

 influence on the photogenic function, and this by maintaining tho 

 vital conditions of the blood and of the tissues ; the nature of the 

 foc<l has no influence on the production of animal light. The cell 

 (the nonsegmented ovum, or the adipose cell) prepares the photogenic 

 principles under the influence of nutrition, but the light is not the 

 direct result of the proper activity of the organized and living ana- 

 tomical element. When the structure of this anatomical element and 

 its vitality are destroyed the luminous phenomenon can still be pro- 

 duced by a physico-chemical action, similar to that which converts 

 glycogen into sugar in the liver. Though the luminous organs of 

 Pyrophorus are the most remarkable known to us, the organic expense 

 is almost insignificant as compared with the effect produced ; so, too, 



