VERTEBRATES: BACKBONE AND BRAIN 107 



is the highest product of evolution. It never has been 

 surpassed — I venture to say it never can be — except 

 possibly by the tape-worms. I can never help think- 

 ing with what contempt these primitive oysters, if they 

 had had brains enough, would have looked down upon 

 the toiling, struggling, discontented, fighting, aspiring 

 primitive vertebrates. How they would have won- 

 dered why God allowed such disagreeable, disturbing, 

 unconventional creatures to exist, and thanked him 

 that he had made the world for them, and heaven 

 too, if there be such a place for moUusks. Their road 

 led to the Slough of Contentment. 



But even in moUuscan history there was a tragic 

 chapter. The squids and cuttle-fishes regained the 

 swimming life, and in their latest forms gave up the 

 protective shell. But its former presence had so modi- 

 fied their structure that any great advance was impos- 

 sible. It was too late. The sins of the fathers were 

 visited upon the children in the thousandth generation. 



The vertebrate developed an internal skeleton. 

 This was necessarily a slow growth, and the type came 

 late to supremacy. The longitudinal muscles are 

 arranged in heavy bands on each side of the back, and 

 the animal swims rapidly. The sense-organs are keen. 

 The brain contains the ganglia of several or many seg- 

 ments and is highly differentiated. It has a special 

 centre of perception, thought, and will ; it is an organ 

 of mind. The vertebrate has the physical and mental 

 advantages of large size. 



First the definite form and mode of developing a 

 vertebra is attained. Then the vertebral column is 

 perfected. The fins are modified into legs. The 

 lungs increase in size and the h^art becomes double. 



