Fishes Photohlepharon and Anomalops. 49 



refractive, but made no chemical tests for guanin. Back of this 

 reflector layer is a layer of cells containing small black pigment 

 granules which effectively screen the tissues of the animal from its 

 own light. In addition, the socket in which the hght-organ lies, the 

 movable screen in Photoblepharon, and the whole of the light-organ 

 except the front, almost flat, surface, are covered with this black 

 pigment layer. 



Just below the front surface of the organ a number of the tubes 

 unite to form a common reservoir which connects with the exterior 

 by a pore (20 to 30 microns wide) passing through cutis and epidermis. 

 The pores are scattered over the surface of the organ and were over- 

 looked in Steche's first description of the tissue. There is no doubt 

 of these pores, however, as they are very clearly visible in sections 

 of the gland made by Professor Dahlgren, of Princeton University. 



At the base, the light-tubes are protoplasmic, but the rest of the 

 tube appears to be one large vacuole of secretion made up in fixed 

 material of small droplets and granules uniformly distributed from 

 base to front of tube. The outUnes of the tubes are so diflScult to 

 see at the front that Steche gained the impression that the cell itself 

 is directly converted into the secretion. Although no mitoses were 

 observed, the appearance of cells with large nuclei at the base of the 

 tube was such as to suggest a growing layer there which supplies 

 new gland-tube cells to take the place of those wasting away by 

 formation of the Hght-giving secretion. No luminous material 

 is passed out of the gland, a point which I can confirm from my obser- 

 vations of the living fish, so that Steche beUeves the light to be burned 

 in the reservoir at the front surface of the gland. The light would 

 therefore be extracellular but intraglandular. 



At the front end of the gland-tubes there is a 1- to 2-layered epi- 

 thelium that passes at the pores into the epithelium of the outer 

 surface of the organ. Here, also, is a tough connective tissue in 

 which are embedded blood-vessels and nerves. The red blood- 

 vessels are very clearly visible in the living organ outhned against 

 the white of the gland. They arise as 9 to 13 vessels passing from 

 both the lower and upper edges of the front surface of the gland 

 and branch to smaller vessels meeting near the middle. A peculiar 

 valve occurs where branch vessels leave the main artery. The 

 blood-supply is exceedingly rich. 



Steche could not determine the point of ending for the nerves 

 which follow the blood-vessels, but thinks they pass to the gland- 

 tubes and control the secretion. I should judge it more likely that 

 they are vasomotor in function, but I have no evidence for this 

 point. The nerve is a large branch of the trigeminal-facial complex. 

 There was no indication of a marked center in the brain, such as that 

 possessed by some electric fishes to control their electric organs. 



