REPORT ON THE DEEP-SEA FISHES. 313 



arc, as is here supposed, phosphorescent ; yet it seems by no means improbable that 

 they are sense-organs. However problematical the function of this part of the organ 

 may be, there can be no doubt that the small spindle-shaped organ attached outside 

 to the scale is phosphorescent. It appears very similar to the suborbital organ of 

 Opostomias micripnus. 



In many of the phosphorescent organs of fishes, glands appear combined with slender 

 spindle- or club-shaped elements which produce light with the aid of tlie secretion of the 

 gland, in which they are immersed. 



The membranes covering these phosphorescent organs in Halosaurus make it appear 

 probable that we have here a similar case. The secretion of the glands observed 

 at the sides and over the slime-canal, and probably also the slime produced in the latter 

 itself, are stored in the lens-shaped spaces of the tissue between the scales and the 

 slime-canal, are then poured into the pockets between the membrane and the scales, 

 and surround the projecting phosphorescent organs, the spindle-cells of which may by the 

 aid of the secretion produce light. The abundance of 1 jloodvessels at the base of the 

 organ and their great size indicate that some very energetic function goes on within it, 

 and we may assume that this function is the production of light. 



e. Development. 



In the various species of Halosmbrus the development of this organ from an ordinary 

 lateral line can easily be traced. It is not indicated in Halosaurus oiveni, and is 

 most highly developed in Halosaurus macrochir. 



This organ is therefore to be regarded as a further development or differentiation of 

 that portion of the lateral slime-canal, with which it remains permanently connected. 



B. Irregular Glandular Organs. 



These are to be distinguished from the preceding group of regular ocellar organs by 

 their larger size, their irregular shape, and particularly by their distribution over the 

 surface of the body, which is never segmental. 



7. Glandvilar organs of irregular position. 



a. Distribution. 



Such organs occur only in Astronesthes niger, and their histology has not been 

 previously investigated. 



(ZOOL. ClIALL. EXP. PART LVII. 1887.) I'll 40 



