PHYSIOLOGICAL LIGHT. 417 



Many Gtenephora, among which may be cited the Cestidce, the Gydip- 

 pidce, the Beroidce, are luminous. The photogenic elements generally 

 surround the costal vascular canals and sometimes also the canals of 

 the gastro-vascular network. The embryo of Berocs, while yet in the 

 egg, is luminous, and usually, if not invariably, photogenic animals 

 transmit from generation to generation the torch of life that is never 

 extinguished and seems to have been lighted at the very dawn of cre- 

 ation. In the Mediterranean the phosphorescence of the sea may be 

 exclusively produced, as I have found, by the disintegration of coelen- 

 terates, whose bodies are sometimes thrown on the shore in great 

 numbers. 



Among the echinoderms the star fishes and particularly the Brisin- 

 gidce furnish most brilliant examples. Certain Ophiuridce also emit a 

 beautiful green light, especially when young. 



Balanoglossus also produces an emerald-green light having a very 

 beautiful effect, aud this function is an additional character connecting 

 that creature with echinoderms and worms. 



In the race of worms the photogenic function has been observed in 

 many wandering annelids. In the collared Polynoe it appears in a 

 quite limited region of the elytra, around the elytrophore, where sec- 

 tions show a structure that recalls that of the luminous organs of 

 Pholas, of which we shall speak further on. 



In other cases the luminosity is situated in the antenna' and its 

 existence has been shown quite early in polytrochous larvre of poly- 

 chcetous annelids. Quite frequently in France there have also been 

 found earth worms, luminous Lumbrici, recently placed in the genus 

 Photodrillus. The species that compose it seem to be of exotic origin. 



Among articulate animals there are a great number of species in 

 which the photogenic function is very well developed and particularly 

 well differentiated. It is in general localized, but often the localization 

 seems to be displaced during the metamorphoses of the individual. 



Many crustaceans have a luminosity of their own. It may be pro- 

 duced as in the Euphausidce, iu quite definite organs, which may have 

 a structure so complex that they have been considered as eyes. This 

 connection of a luminous organ appears less strange when we know the 

 mechanism of the dermatoptic and photogenic functions in Pholas dac- 

 tylus, and, besides, it is not impossible that the same organ may alter- 

 nately or simultaneously perform two functions. These luminous 

 globules or photospheres may exist at the same time in various parts 

 of the body, on the claws, the thorax, the abdomen, etc. In other 

 Crustacea, such tisMysis, there is a brilliant circle surrounding the eye, 

 which is actually set in a luminous, spherical cavity. The photogenic 

 power of the eyes appears to be well developed also in Aristeus, Geryon, 

 and Munida. 



In the class of Myriapods luminosity has been scientifically investi- 

 gated among the Geophilidw iu both sexes of iScolioplanes crassipes. 

 SM 95 ,27 



