74 EVOLUTION 



most beautiful illustrations of the theory of evolution ; 

 but I must send the reader to the pages of Professor 

 Le Contes' Elements of Geology (last edition, revised by 

 Professor Fairchild) for the lengthy story of the cuttle- 

 fish, etc. The Echinoderms appear in successively 

 higher forms, and the evolution of the different orders 

 has been well traced by Professor MacBride (in the 

 Cambridge Natural History). Probably all come from a 

 primitive stalked form. The rays of the star-fish retain 

 the flower-like spread of the arms, and in the sea-urchin 

 these rays are curled up into a ball. More difficult is 

 the evolution of the "worms" (now split into a bewilder- 

 ing classification), while the infinite variety of the 

 Arthropods must be respectfully set aside in so short a 

 sketch as this. Under this great group are comprised 

 the aquatic Crustacea (water-flea, cyclops, lobster, crab) 

 etc.), and the air-breathing Tracheates (centipedes, 

 spiders, and the innumerable insects). 



To attempt to sketch even superficially the way in 

 which this vast and varied kingdom spread over the 

 shores, the land, and the fresh waters of the rising 

 continents, would be a lengthy and very difficult and 

 precarious task. Curiously enough it is a fine illustra- 

 tion of the law that the individual must pass to some 

 extent through the forms of his ancestors the members 

 of this group that now seem farthest removed from the 

 denizens of the sea still retain a most striking proof of 

 their origin. I refer to the metamorphosis of the insect. 

 The graceful dragon-fly seems hopelessly removed from 

 the worm-like creatures of the pre-Cambrian ocean 

 until you catch him in his early stages in the pond. 

 Indeed, the order in which the insecte make their 

 appearance in the geological record is encouraging 

 enough to the evolutionist. The first trace we have of 

 them is a stray wing in the middle of the Silurian (more 



