590 SUPPLEMENT ON POLYPI. 
successively by the sea, as is the case in our northern seas. 
Some of them attain great dimensions, having been found 
more than three or four feet in height. We are not exactly 
acquainted with the duration of their life, nor with the degree 
of rapidity in their growth ; but we must conclude that they 
grow promptly if it be that they can be fished for, with suc- 
cess, after the second year, in places which had been previ- 
ously exhausted of them. ‘The sponges are very common in 
the seas of warmer climates, where they attain the largest di- 
mensions. They are less so in those of temperate regions, 
and finally, as we approach the ices of the north, they become 
more and more rare, and smaller, and utterly disappear near 
the polar circle. 
