HYDROZOA. 



43 



vine, which twining round some foreign object, hold 

 the little bark secure. When no longer wanted, 

 shrinking back into itself, this apparatus vanishes 

 from view, leaving no trace of its existence. 



Minuter forms of these Beroes throng the icy seas 

 in countless myriads, and their abundance and ex- 

 ceeding beauty have attracted the attention of all 

 northern voyagers. Great shoals of them are there 

 met with, discolouring the water for a vast extent. 

 Scoresby observed, that the colour of the Green- 

 land sea varies from ultramarine blue to olive green, 

 and from the purest transparency to striking opacity, 

 ajjpearances which are not transitory but permanent. 

 The green semi-opaque water mainly owes its singu- 

 lar aspect to minute Beroes and Infusorial animal- 

 cules. It is calculated to form one-fourth part of 

 the Greenland seas, between the parallels 74° and 

 80°. It is liable to alterations in its position, from 

 the action of currents, but it is always renewed near 

 certain situations from year to year. The whales 



'>*^ 



Fig. 28.— food of thk whale : 

 , Limacina helicina ; 2, 3, 4, Medusa; ; 5, Clio borealis. 



throng in this opaque water, for to them it is a good 

 wholesome . soup, nourishing enough, as may be 

 judged from the following curious calculation : — 

 " The number of Medusae," writes Mr. Scoresby, '' in 

 the olive green water was found to be immense. They 

 were about one-fourth of an inch asunder. In this 

 proportion a cubic inch of water must contain 64 ; 



