HISTORY OF CCELENTERATES. 145 



Medusoid (Livmocodium) found in a tank at Kew. Most of 

 the active swimmers live near the surface, but there are also 

 deep-water inhabitants of active disposition. Many polypes 

 anchor upon the shells of other animals which they some- 

 times mask, and there are most interesting constant partner- 

 ships between hermit-crabs and sea-anemones. The reef- 

 building corals fringe the coasts, or rise upon the tops of 

 submarine volcanoes, but nowadays they are restricted to an 

 equatorial zone, whose boundary lines are marked by a 

 minimum average temperature of 60^ Fahr., nor are they 

 ever found alive at depths exceeding twenty fathoms. The 

 red-coral of commerce is obtained from the Mediterranean 

 and from the Atlantic off the N.W. of Africa. 



As to diet, the active Ctenophores are carnivorous, 

 attaching themselves by adhesive cells to one another or to 

 other small animals; many of the larger forms, e.g., sea- 

 anemones and jellyfish, are able to engulf booty of 

 considerable size ; the majority, however, feed on small 

 organisms, in seizing and killing which the tentacles and 

 stinging-cells are actively used ; but what the corals eat no 

 one seems to know. 



History. — Of corals, as we would expect, the rocks pre- 

 serve a faithful record, and we know, for instance, that in 

 the older (Palaeozoic) strata, they were represented by a 

 distinct series {Rugosa or Tetracoralla), of which we have 

 now only two or three survivors. We often talk of the 

 imperfection of the geological record, and rightly, for much 

 of the library has been burned, many of the volumes are 

 torn, whole chapters are wanting, and many pages are 

 blurred. But this imperfect record sometimes surprises us, 

 witness the quite distinct remains of ancient jellyfish, which 

 animals, as we know them now, are blubber-like and appar- 

 ently little more than animated sea-water. It is right, too, 

 that we should grasp the conception, with which Lyell first 

 impressed the world, of the uniformity of natural processes 

 throughout the long history of the earth. Thus, in connection 

 with Coelenterates, we learn that there were great coral reefs 

 in the incalculably distant past, just as there are coral reefs 

 still. So in the Cambrian rocks, which are next to the 

 oldest, there are on sandy slabs markings exactly like those 

 which are now left for a few hours, when a large jellyfish 



K 



