194 THE MECHANICAL FUNCTIONS. 



the ocean.* In some parts of the Greenland 

 seas they swarm to such an extent that they 

 give a visible tinge to the colour of the waves for 

 hundreds of miles. The total number of these 

 animals dispersed over that space surpasses the 

 utmost stretch of the imagination. In these 

 situations a cubic foot of water, taken indiscri- 

 minately, was found by Mr. Scoresby to contain 

 above 100,000 of these diminutive medusae. 



Belonging to the tribe of Medusaria is a sin- 

 gular genus, denominated the Bcroe, (Fig. 82 

 and 83,) which is remarkable for its organs of 



82 



progressive motion. Its body is either globular, 

 or oblong, and it swims with its axis in a vertical 

 position. Eight longitudinal bands or ridges, 

 which have been sometimes compared to ribs, 



* The luminous property of sea water, or its phosphorescence, 

 as it is sometimes called, generally arises from the presence of 

 minute medusae, which are met with in greatest numbers at the 

 surface, being specifically lighter than the surrounding fluid. 



