JURA. LUMINOUS ANIMALS. 



property. The third and last cause which has tended 

 to deceive naturalists and conceal these animals from 

 observation, is that property which so many marine worms 

 possess of speedy solubility in sea water after death. The 

 small time occupied in effecting the solution and total 

 disappearance of even the larger kinds, gives reason to 

 suppose that the smaller have often eluded investigation 

 from the extreme rapidity with which they undergo this 

 process ; a supposition the more probable, when we con- 

 sider the circumstances under which these examinations 

 are generally made. 



With respect to the nature of the light, it is important 

 to remark, that it appears in two distinct forms, and in 

 these cases apparently arising from two sources. The 

 twinkling appearance seems always to proceed from the 

 animals, and to be the result of their own actions. It takes 

 place when the water is at rest, and is much brighter 

 than the light produced by merely disturbing the water 

 where these are not present. On examining them, they 

 are frequently found covered with luminous points ; and it 

 was ascertained by Professor Smith, that the seat of 

 the light in one species of Cancer was in the brain ; while 

 it was apparently also under the influence of the animal. 

 The fainter diffused light appears to originate rather from 

 detached luminous matter dispersed through the water. 

 This appears however to abound exactly in proportion to 

 the number of marine animals present ; and hence it is so 

 remarkable in those seas where the worms and insects are 

 most plentiful. This matter seems often to be the cause of 

 the light produced by friction or agitation; although it 

 is certain that the same disturbances also cause the 

 marine animals to give out their own light. To Pro- 

 fessor Smith it appeared that this substance consisted of 

 solid spherical particles ; but it may be questioned whe- 

 ther these were not rather animalcules, or perhaps the ova 

 of the worms or insects which were present. 



It is next necessary to inquire to what extent this 



