14 TEE ZOOLOGIST. 



in alcohol, essence of petroleum, benzine, and ether, which he 

 called luciferine ; the other albuminoid, which he termed luci- 

 ferase. As this mollusk — the "Pierce Stone" of Petiver — in- 

 habits the holes it bores in rocks, and lives on minute forms 

 carried in by the branchial current, it would be difficult to frame 

 any theory — on the basis proposed by the naturalists of the 

 ' Porcupine ' — which could be adapted to it. 



Several Pteropods are likewise luminous, according to Giglioli, 

 viz. a Cleodora, which gives out a vivid reddish light, a Creseis, 

 and a Hyalcea, which are phosphorescent at the base of the 

 shell. An unknown Heteropod in the Indian Ocean also glowed 

 with a reddish phosphorescence. The curious Phyllirhoe, a 

 pelagic Opisthobranch, which is found in the Atlantic, in the 

 Pacific, and in the Mediterranean, presents (in P. bucephala of 

 the latter sea) a vivid azure luminosity, chiefly at the superior 

 and inferior borders of the body, but no luminous mucus is 

 exuded. Panceri considered that the contents of certain cells 

 (cells of Muller) placed in the vicinity of fine nerves produced 

 the light under the action of a stimulus. 



In the highest group of mollusks, viz. the Cuttle-fishes, phos- 

 phorescence occasionally occurs. Giglioli observed that Loligo 

 sagittatus and a small Octopus gleamed all over with a whitish 

 luminosity. The same has been noticed in Cranchia scabra, 

 Leach. 



The Tunicates or Urochordates show several striking examples 

 of luminosity. Thus Agassiz and Giglioli found the notochord 

 of an Appendicularian glow with a rich red, then azure, and 

 finally with green. No luminous British form has yet been 

 observed. One of the best known, however, is Pyrosoma from 

 the warmer seas, so graphically described by Peron, Huxley, 

 Panceri, and others, and one gigantic example of which was found 

 by the ' Challenger ' four feet in length. This colonial yellowish- 

 white form, under irritation, glows with red, golden, orange- 

 green, and blue, the light proceeding in each member of the 

 organism from two small oval patches of cells at the base of each 

 inhalent tube. These cells contain substances resembling fat 

 and albumen, and their membranous sheath is bathed by the 

 blood of the lacuna. The luminosity ceases with the life of the 

 colony. Salpa, also, is usually classed amongst the luminous 



