THE SHORES OF BKITAIN. 55 



succession, opaque masses, which it strewed every- 

 where around. The beauty and novelty of such a 

 scene in the animal kingdom long arrested my at- 

 tention ; hut after twenty-five minutes of constant 

 observation, I was obliged to withdraw my eye, from 

 fatigue, without having seen the torrent for one 

 instant change its direction, or diminish in the 

 slightest degree the rapidity of its course. I con- 

 tinued to watch the same orifice, at short intervals, 

 for five hours, sometimes observing it for a quarter of 

 an hour at a time ; but still the stream rolled on 

 with a constant and equal velocity." 



Sponges, in general, appear to have little choice of 

 situation, but to grow wherever the young offset or 

 gemmule happens to drop, whether on the rock, on a 

 shell, or on a sea-weed. If two of the same species, 

 growing side by side, come into contact, their edges 

 unite, and the two form one mass, so perfectly one 

 that the most practised eye could detect no indication 

 of the Ime of union. On the contraiy, if the neigh- 

 bours be of different species, the edges adhere by 

 contact, but there is no union ; and both of the con- 

 tiguous edges will grow up far beyond their natural 

 level, like walls striving to overtop each other, until 

 the action of the waves prevents the continuance of 

 a mode of growth so unnatural. Dr. Johnston speaks 

 of two species of Sponge, which had become so inter- 

 mingled in growth, without being united, that, being 

 of different colours, they presented tlic appearance of 

 a coloured map. The same writer has ligured a much- 

 branched species {Haliclwndria oculata), growing on 

 tlie tack of a small crab ; the latter has a grotesque 



