256 Remarks on Marine 



Nereides, and many others, which make these places their ex- 

 clusive residence. 



It is now necessary to point out the method used in examining 

 these animals, and deciding on their luminous powers. 



With respect to the larger kinds, there is no difficulty ; the 

 smaller require many more trials ; and where more than one 

 species persist in occurring together, some uncertainty must 

 always remain. Yet where a property is, in so many instances, 

 ascertained to exist, and where it has probably been conferred 

 for the specific purposes formerly noticed in the essay to which 

 this communication must be considered as an appendix, it is 

 not a rash conclusion to consider that no species is exempt from 

 the general law or deprived of this power ; since in the most 

 essential circumstances, the habits of all are the same. 



These animals, whether the smaller vermes or insects, are 

 very rarely found in clear water, and wherever they are abun- 

 dant it is muddy, or rather fouled with some animal matter 

 which communicates to it a slight milky hue ; although they are 

 not, on the contrary, necessarily present when the water is in 

 that state. It is preferable to examine the water by candle- 

 light, as ordinary day-light is not sufficient for the purpose; 

 and the light of the sun cannot easily be received in such a manner 

 as to be endured by the eye, and, at the same time, to serve the 

 purpose of illuminating the objects. It is desirable to use more 

 than one candle, as it is convenient to have more than one lu- 

 minous spot under command; the rapidity of the motions of most 

 of these animals, carrying them so quickly beyond the limits of 

 one spot, as to cause considerable trouble to the observer, who 

 has many things to distract his attention at the same time. 

 Some of them are better examined in the brightest light ; others 

 at its borders ; and, very often, it is necessary to examine the 

 same object in different lights before a just idea of its form can 

 be obtained. A separate light is also required to illuminate the 

 paper on which they are to be drawn ; the eye being so far 

 paralyzed by the excess of light required to view them, as not 

 to see in a moderate degree of illumination, and it being abso- 

 lutely necessary to draw them, without losing the least prac- 



