PHOTOGENIC MARINE ANIMALS. 9 



and now and again breaking into long avenues of vivid light, 

 indicating the paths of fishes and other wandering denizens of 

 these enchanted regions. 



There are comparatively few luminous members of the group 

 of Echinoderms, the most conspicuous being the common Brittle- 

 star (Ophiothrix) , and one or two allied genera, besides the 

 curious Brisinga. Sir Wyville Thomson describes the light of 

 Ophiacantha as of a brilliant green, coruscating from the centre 

 of the disc along the rays, and illuminating the whole outline of 

 the Star-fish. The common Brittle- star from deep water gleams 

 all over the trawl-net with a pale greenish light, but the adults 

 between tide-marks show no trace of luminosity. The light 

 from a hundred examples of Brisinga is very brilliant. The 

 naturalists of the ' Porcupine ' were of opinion that the young 

 stages of certain Star-fishes were more luminous than the adults 

 in order to act as a check on their increase, but the condition in 

 non-luminous Star-fishes and in other young invertebrates would 

 seem to throw doubt on this view. There are no data, indeed, 

 to show that a luminous form is more eagerly preyed on than 

 one which is not. 



Phosphorescence is stated to occur in certain Planarians and 

 Rotifers, and a species of Sagitta ; but it does not appear to be 

 a common manifestation in the lower worms. On the other 

 hand, the luminosity of the Annelids is brilliant, and has been 

 noted from early times. The representatives of five families of 

 Annelids possess this property, yet there is nothing specially 

 different in the habits of these from those in which this feature 

 is absent. In the family of the Polynoidce no less than six or 

 seven British species are phosphorescent. One of the most 

 abundant between tide-marks is Polynoe floccosa, which emits 

 greenish scintillations from the point of attachment of the scales, 

 and in a double moniliform line along the ventral surface. It 

 lives under stones. Others, such as Gattyana cirrosa and Polynoe 

 scolopendrina, frequent the tubes of Terebellids, whilst Achloe 

 haunts the ambulacral grooves of Star-fishes (Astropecten). 

 Though Dr. Jourdan is of opinion that in Polynoe torquata the 

 luminosity is produced by cells secreting mucus, it would appear 

 that in the majority of the Polynoidce no secretion of mucus is 

 present. It may be that, as Watase observes, the light-giving 



