THE CYDIPPE. 327 



the point is still sub judice. It is only since the beginning 

 of this century that the attention of naturalists has been 

 fixed upon the Noctilucm as sources of the phosphorescence, 

 in all times observed, and in former times attributed to the 

 presence of decaying organic substance, to electricity, to 

 " an absorption of solar light disengaged in the dark," &c.* 

 The extensive and minute investigations of M. Quatrefages 

 led him to the following conclusions : 



There are two different kinds of phosphorescence observed 

 in the sea. The first is of very brilliant but isolated sparks, 

 and is due principally to Star-fishes, Crustaceans, and Anne- 

 lids. The second is of a general luminous tint, over which are 

 strewed isolated sparks, and is due to the Noctilucse. These 

 Noctilucce have no special organ which produces the phos- 

 phorescence as the other animals have ; but the light emanates 

 from the whole substance of their bodies. Every irritant, no 

 matter of what nature, produces this phosphorescence in them. 

 The phenomenon is not, as in insects, one of combustion ; but 

 is intimately connected with the contraction, spontaneous or 

 provoked, of their substance. It is independent of all secretion, 

 and it is probable that the sparks are due to the ruptui-e and 

 sudden contraction of their sarcodic filaments ; while the 

 steady light they emit in dying results from the permanent 

 contraction of this sarcodic substance. 



Having satisfied curiosity about the Noctilucce, let us turn 

 once more to the Cydippes, which should be placed in the 

 tallest jars, because, while the Medusae keep at the surface, 



* For the history of these opinions, and other curious details, see the M€moire 

 of M. Quatrefages, Annates des Sciences. 1850. 



