THE VICTORIAN NATURALIST. 101 



living in the depths in many ways, of which probably the most 

 interesting is in enabling them to manufacture their own light. 



Up to the present time very little work seems to ^ have been 

 done on the phosphorescent organs of the higher Crustacea. 

 Sars (30), of course, who described the Challenger Crustacea, 

 mentioned them, and Dr. Alcock (2), who was surgeon-naturalist 

 on the Investigator for four years, observed them, and recorded 

 their appearance. "On one occasion," he writes, "three large 

 specimens of luminous Crustaceans were brought on board alive, 

 one of which, Heterocarpus, was most brilliant, and both sexes of 

 which poured out, apparently from the orifices of the green 

 glands at base of the antennae, copious clouds of a ghostly 

 blue light, of sufficient intensity to illuminate a bucket of sea 

 water, so that all its contents were visible in the clearest detail." 



In some of the deep-sea Crustaceans the luminous apparatus 

 takes the form of pale red spots with a central clear nucleus. 

 The phosphorescence proceeds from the red pigment surrounding 

 this nucleus. The body of the nucleus is very mobile, and is 

 described as a true lens, acting as a condenser, and by this means 

 the animal is enabled to produce a bright flash of light in a given 

 direction. 



In the case of the phosphorescence of fish more work has 

 been done, and the researches of Von Lendenfeld (36), 

 Giinther (14), Professor Moseley (27), Sir Wyville Thomson (33), 

 and many others enable us to understand, to some extent, the 

 structure of the luminous organs and glands. 



In the simplest cases we find that the mucous glands, to be 

 seen in most fish, are especially strongly developed, and that 

 their secretion is luminous. In such cases the fish must show a 

 continuous phosphorescent glow on the head, or head and neck, 

 where the mucous canals are most abundant. The light 

 produced in this way is probably not under the control of the 

 animal. Such a fish was obtained by Alcock in the Laccadive 

 Sea — Aulastomorpha. 



Other fish have definite organs, which may be present in every 

 gradation of structure from a small luminous patch of skin on the 

 head up to the complicated organs placed in the side of the body, 

 which resemble " bull's-eye lanterns." Some fish have organs in 

 addition to the luminous secretion, and these are not necessarily 

 all of the same structure in the same fish. Photostomias shows a 

 phosphorescent patch on the cheek, and the organs arranged in 

 two rows on each side of the body. 



In one fish, Astronesthes, described by Von Lendenfeld in the 

 Challenger volume, there are small phosphorescent organs on the 

 side of the head of a very simple structure, luminous patches near 

 the top of the head, and both simple and compound organs as 

 well ; the former having glandular cells which secrete mucous 

 material and are covered by a transparent patch of skin. Behind 



