126 LECTURE x. 



no appearance of any regular viscera or inter- 

 nal organs, but the whole presents a continued 

 vacuity. The colour of this curious animal, when 

 at rest, is a pale greenish blue ^ but when in mo% 

 tion, which is performed by the alternate con- 

 traction and dilatation of the body, the whole 

 appears in the highest degree of phosphoric lustre, 

 passing through all the colours of a bar of red- 

 hot iron, till at length it becomes of what is term- 

 ed a white-heat ; after which it again passes into 

 the colour of red-hot iron, and from that gra- 

 dually declines into its original greenish hue. The 

 length of this animal is that of several inches, and 

 its diameter about a fourth or fifth of its length. 

 It is a native of some particular parts of the At- 

 lantic Ocean, where it is seen in great multitudes, 

 and irradiates the waves with its fiery brilliancy. 

 Linnaeus would perhaps have been inclined to have 

 made it a species of Holothuria. 



In the enlarged edition of the Sy sterna Natu- 

 rae by Gmelin, some of the small fresh- water spe- 

 cies of the Linnaean genus Nereis are more pro- 

 perly referred to a new and distinct genus, under 

 the name of Nats. As an example of this genus 

 jnay be mentioned a very small, transparent, and 



