48 The Production oj Light by the 



In life, the light of Anomalops is constantly being turned on and off, 

 according to Steche, 10 seconds light and 5 seconds dark. Photo- 

 hlepharon in its natural environment shows its light continuously, 

 but in glass jars, either as a result of partial asphyxiation or excite- 

 ment, its light is also intermittent. The animals appear to be swim- 

 ming about with bright flash-lights which are turned on periodically. 

 According to the natives, the use of the organ is as a search-light. 

 Its use, according to Steche, is as a " Scheinwerfer" or search-hght 

 to attract prey, and the flashing is to mislead its prey. 



When brought into the laboratory, in small glass jars, where the 

 supply of air is limited, the fish lose control over the closing mechan- 

 ism and the flashes become irregular. Just before death from asphyx- 

 iation, when the fish swim upside down and slowly, the light is 

 usually not visible, but on actual death, when movement ceases, 

 the organ is exposed and gives forth light, both in Anomalops and 

 Photoblepharon. This simply means that the muscles involving the 

 closing mechanism pass into the relaxed condition on death. The 

 relaxed condition of these muscles, then, corresponds with the exposed 

 position of the organ. 



HISTOLOGY OF THE LIGHT-ORGAN. 



Although this paper deals with the chemistry of light-production 

 in Anomalops and Photoblepharon, an accurate description of the 

 structure of the organ is of considerable interest in view of the rather 

 startling conclusion to which I have come from chemical investiga- 

 tion, namely, that the Hght-organ is a mass of tissue designed for the 

 nourishment of luminous bacteria, which produce the Hght. The 

 gross anatomy and histology of the organ is the same in both fishes, 

 with the exception of the movable screen to obscure the light, pos- 

 sessed only by Photoblepharon. 



Steche describes the organ as an acinose gland made up of a large 

 number of gland-tubes parallel to each other and extending completely 

 across the organ, from the back pigmented surface to front trans- 

 parent surface, where the light emerges. The ascini have been 

 elongated and arranged parallel to each other. In a parallel section 

 of the fresh organ it is very easy to see these tubes and also the blood- 

 vessels which run between them. A cross-section of the tubes shows 

 that they are pressed into a polygonal shape, separated from one 

 another by sparse connective tissue and arranged in a ring about a 

 blood-vessel, whence they get their oxygen and food-supply. The 

 back ends of these tubes meet a layer of cells containing small gran- 

 ules of guanin, which are believed to act as a reflector layer, in analogy 

 with such a layer found in the luminous organs of other fish. Steche 

 observed that these granules dissolved in formalin and were doubly 



