12 THE ZOOLOGIST. 



mud, so that .its luminosity is useless to itself in procuring food ; 

 and, since the animal is, as it were, all slender legs, with a span 

 of nearly twenty inches, it would not form a tempting bait for 

 any fish. Dr. Alcock* placed it ventral surface upward in a 

 dark cabin, where it shone like a star, the body and all the legs 

 except the egg-bearing pair showing as lines of persistent blue- 

 green light. This gradually died away, but remained, for a long 

 time illuminating the long fifth and sixth segments of all but the 

 first pair of legs. The theory of the ' Porcupine ' naturalists 

 gains little support from this form. 



Occupying a similar position to the myriads of other Arthro- 

 poda, such as insects, spiders, and centipedes on land, the group 

 of marine crustaceans rivals them in the enormous numbers of 

 its representatives. Amongst these luminosity occurs in the 

 minute Copepods (whose vast numbers and ubiquitous distribu- 

 tion make them so important in connection with the nourishment 

 of young fishes and even of Whales), in Sapphirina, a member of 

 the same group, in various Schizopods, and in the higher or 

 decapod crustaceans. In some of the minute types, such as the 

 Copepods, the phosphorescence has been attributed to the food 

 in the interior. In a similar way the luminous Sandhopper 

 (Talitrus) was found by Giard to have photogenic Bacteria para- 

 sitic in its abdominal cavity, and they by and by entered the 

 organs, causing its death. During the disease the animal 

 emitted a green light, which ceased a few hours after death. In 

 the Schizopods the Opossum Shrimps (Mysidce), Euphansia, and 

 Lophogaster (Gnathophansia) have luminous organs, which have 

 often been regarded as eyes. They have bright red pigment, 

 and are situated on the thorax and abdomen. Sarst describes 

 the essential part as the fibrous fascicle lying in the centre of 

 the globular corpuscle. The lenticular corpuscle placed just in 

 front of this acts as a condenser, and a glistening ring round the 

 lens resembles an iris. Muscles, moreover, move the organ. 

 The diaphanous front and the red pigment of the posterior part 

 also lead to the assumption of the close resemblance to a verte- 

 brate eye. He, however, found, on experimenting with the living 

 animal, that they had nothing to do with vision. Perrier, on the 



* 'Zoological Gleanings,' 1901, p. 74. 

 f 'Challenger,' vol. xiii. 



