OF CREATION. 



37 



organization and of which only the hard external 

 coat is preserved, or speculate with regard to its food 

 and its method of obtaining it. From the absence of 

 antennae, however, and the want of powerful extre- 

 mities, as well as from the manner in which these 

 fossils are found,* the different species probably 

 lived for the most part in shallow water, not buried 

 in mud, but floating near the surface with their under 

 side uppermost, feeding on the minute and perhaps 

 microscopic animalcules that usually abound in such 

 localities. There are several natural groups, marked 

 by differences somewhat considerable, but the number 

 of species is not great. 



The most remarkable point with regard to these 

 trilobites is the presence of the large compound eyes 

 with which they were provided. These eyes appear 

 to be constructed on the same principle as those of the 

 dragon-fly and other insects : they are ranged round 

 about three-fourths of two conical projections rising 

 one from each side of the head, and they are so 

 placed that the animal, without moving from the spot 

 in which it might be, could see in all directions around 

 it. It appears, from this perfect and complicated con- 

 trivance, that, at the earliest period of the introduction 

 of animals, the general conditions of light and the 

 atmosphere could not have differed in any important 

 degree from those which now obtain. 



Together with the graptolites, the corals, the en- 

 crinites, and the trilobites, there seem to have existed 

 as contemporaries, two, or perhaps three, very re- 

 markable tribes belonging to the great natural group 



* They seem to have been very gregarious, living by thousands in a 

 single locality, and often heaped upon one another. 



