44 HYDROZOA. 



a cubic foot, 110,592 ; a cubic fathom, 23,887,872, 

 and a cubical mile about 23,888,000,000,000,000! 

 From soundings made in the situation where these 

 animals were found, it is probable that the sea is 

 upwards of a mile in depth ; but whether these 

 substances occupy the whole depth is uncertain. 

 Provided, however, the depth to which they extend 

 be but two hundred and fifty fathoms, the above 

 immense number of one species may occur in a space 

 two miles square. It may give a better conception 

 of the amount of Medusae in this extent, if we calcu- 

 late the length of time that would be requisite with 

 a certain number of persons for counting this num- 

 ber. Allowing that one person could count a million 

 in seven days, which is barely possible, it would 

 have required that eighty thousand persons should 

 have started at the creation of the world to complete 

 the enumeration at the present time." 



The Medusas in question were Beroes, called 

 " Fountain-fishes " by the earlier voyagers to Spitz- 

 bergen, who, mistaking the cause of the eight bands 

 of iridescence gleaming along the sides of their 

 bodies, fancied they were so many rivulets of lustrous 

 water. 



In a third form of these beautiful creatures, hence 

 denominated 



Hydrostatic Acalephse, the animal is supported in the 

 water by a very peculiar organ, or set of organs, consist- 

 ing of one or more bladders filled with air, which are 

 appended to the body in various positions, so as to act as 

 floats of sufficient buoyancy to sustain the creature upon 

 the surface of the sea. 



' The Physalia* (Fig. 29), known to sailors by the name of the 

 Portuguese man-of-war, has this swimming apparatus single and of 

 great proportionate size, so that when full of air it is exceedingly 

 buoyant, and floats conspicuously upon the waves. It closely re- 

 sembles, when seen from the deck of a vessel, a child's mimic 

 ship with its sails set; and excites the wonder of those who behold 

 it, to see so delicate and frail a bark breasting the billows, as it 

 seems that the first breaking sea must inevitably overwhelm and 

 dash it to pieces. Yet there it floats, and dances now on the curling 



s, phusalis, a bladder. 



