FIEST FORMS OF LIFE. 



33 



FIG. 8. 



fibres. Its destiny is to remain fixed at the bottom of deep 

 seas, and live upon nutritive particles which it collects by means 

 of an apparatus connected with 

 two spiral-shaped arms, extending 

 from the margin of the mouth, and 

 from which the order has received 

 its name. So prominent does the 

 order appear in this part of crea- 

 tion, -that an eminent geologist 

 distinguishes the Lower Silurian 

 period as the Age of Brachiopods. 



The next most conspicuous fossil 

 is a crustacean, also humble in its 

 class. This is the Trilobite, a 

 marine animal to which the wood- 

 louse makes the nearest approach 

 in general figure, but marked by 

 two groovings along the length of 

 the body, so as to present a tri- 

 lobed form ; hence the name. The 

 king-crab (limulus), an animal of 

 our present seas (Fig. 51), is, in 



an early stage of its existence, somewhat like the trilo- 

 bite. It is surprising how many species and even genera of 

 this form lived in the Silurian seas, and in what quantities 

 their remains are found in various parts of the earth. The 

 means of locomotion possessed by the animal are not known ; 

 but from its form we must suppose it to have lived at the 

 bottom of the sea, having its eyes directed upwards and side- 

 ways. The latter organs presenting facets such as are seen 



FIG. 9. 



Ogygia Buchii, a Lower 

 Silurian Trilobite. 



Facetted eye of Asaphus caudatus. 



upon similar animals of our era, we may be said to have a 

 proof furnished to us by this humble creature, " that the water 

 of those oceans and the supernatant atmosphere, was as trans- 



D 



