46 DOCTRINE OF EVOLUTION 



with highly developed hinder limbs. The salamanders 

 differ as regards the number of fishhke gill clefts that 

 they all possess in their young stages, but which dis- 

 appear entirely or in part during later life. In com- 

 parison with the lizard as a typical reptile, a salamander 

 is more primitive in all of its inner organic systems, 

 while in its nearly continuous body, with head and tail 

 gradually merging into the trunk, it also displays a 

 somewhat simpler form of body. 



The fishes are the lowest among the common verte- 

 brates, and they offer an abundance of independent 

 testimony as to the truth of the principles of compara- 

 tive anatomy. The common shark is perhaps the most 

 fundamental form, with a hull-like body undivided into 

 head, trunk, and tail, and from it have originated such 

 peculiar variations as the hammerhead and skate. 

 Among fishes with true bones, a cod or trout is the most 

 typical in general features. Without ceasing to be 

 true bony fishes, the trunk-fish and cow-fish are adapted 

 by their peculiar characters of spine and armor plate to 

 repel many enemies. The puff fish can take in a great 

 amount of water, when disturbed, so as to become too 

 large to be swallowed by some of its foes, illustrating 

 another adaptive modification for self-defense. The 

 wonderful colors and color patterns of the tropical 

 fish of the reef, or of the open water forms like the 

 mouse-fish of the Sargossa Sea, often render them more 

 or less completely hidden from the foraging enemy. A 

 flounder looks like a fish which was originally symmetri- 

 cal, but which had come to he flat on its side upon the 

 bottom, whereupon the eye underneath had left its 

 original place to appear on the upper surface. The 



