32 THE ORIGIN OF MAN 



in those of brackish water and as they are asso- 

 ciated with the eurypterids it would thus seem to 

 indicate a littorial habitat. As the scorpions are 

 carnivorous animals and as there was, at this time 

 no life except that of the invertebrates, on what 

 did they feed? But as spiders are closely related 

 to scorpions and as species of the former are 

 known to inhabit the sea coasts, it is safe to say 

 that scorpions did likewise, feeding on the small 

 invertebrates, among them trilobites and small 

 crustaceans. 



As the fishes, because they were the first verte- 

 brates and therefore the ancestors of the verte- 

 brates of todaj% require a somewhat lengthy dis- 

 cussion, it will be advisable to make a careful 

 study of them now before we enter the Devonian 

 period, as they first became prominent during 

 the Upper Silurian. Fishes are veterbrates with- 

 out a movable neck and with a distinct and hinged 

 lower jaw. As they all, with a few exceptions, 

 pass their whole life in water, they all have gills 



