98 THE VICTOHIAN NATURALIST. 



he could form no theories as to the use of the Hght. The larva 

 of this insect was found suspended on a web hung across rocky 

 niches on the b^nks of streams in dense forests. A number were 

 found by Mr. Hudson in the Wellington Botanical Gardens, and 

 were reared by him. In this larva there was a luminous organ 

 situated at the posterior end, the shape of which could be 

 ciianged by the animal, and the amount of light emitted seemed 

 to be under its control. In iS86 he obtained a luminous pupa 

 suspended in one of the webs, but the light given by this was 

 much fainter than in the larva. In April, 1889, Mr. Hudson 

 succeeded in obtaining the fly, and in August, 1890, he actually 

 saw a fly standing on the pupa with part of its abdomen still 

 within the pupa skin. Wiien the fly finally emerged it gave out 

 a very strong light from the abdomen, which brilliantly illum- 

 inated the box in which Mr. Hudson had placed it. 



Let us now turn our attention to the perhaps more interesting 

 cases of phosphorescence shown by animals in the sea. It need 

 hardly be said that the examination of these animals is beset by 

 many difficulties. In the case of the more minute organisms, 

 even if one is provided with a microscope, the phosphorescent 

 water probably contains so many forms that to be distinguished 

 they must be seen by a strong light, and then, of course, it is 

 impossible to tell which are and which are not luminous. Again, 

 difficulty occurs in the case of large animals living in the sea, 

 especially those from the abysmal depths, such as deep sea fish 

 and crustaceans. These are extremely difficult to obtain, and 

 when they have been dredged the conditions under which they 

 are viewed are so altered as to make it well-nigh impossible to 

 judge of their behaviour in the natural state. 



The phosphorescence of the sea (27, "■Challenger Narrative," 

 vol. i.) attracted much attention about the beginning of the i8th 

 century, and many explanations of it were attempted. In 1690 

 Tachard, a priest, explained the matter by stating that the waters 

 of the ocean absorbed sunlight by day and gave it out again at 

 night. Newton, 1730, considered that it was caused by the 

 continual agitation of the waves. Some thought that it was due 

 to a self-luminous substance, others to decayed material, while 

 still others ventured the opinion that the phenomenon was pro- 

 duced in some unknown manner by living organisms, and this 

 last suggestion, by discoveries made since, has been fully verified, 

 whereas the other theories have one by one been disproved. 



The lights seen at night from a ship at sea are chiefly due to 

 animals which float and drift about on the surface of the ocean. 

 •' It is not," says Hickson (16), "as is very commonly supposed, 

 only one or two diff^erent kinds of animals that are phosphores- 

 cent, but a vast number, belonging to many widely different 

 families and of great variety of form and structure." 



