THE EVOLUTION OF LIFE AND MIND 81 



find the primitive ganglion communicating by threads with 

 sensitive depressions in the skin of the head (the rudiments 

 of the eyes, ears, and nose-pits) ; and we find it extending 

 along the back (some suggest that it crept along a discarded 

 alimentary tube). While this extension grows into the 

 spinal cord, the important bulb at the front, the intelligence- 

 department of the animal, with its advanced sentinels, the 

 sense-pits on the face, are bound to be continuously 

 advanced by selection. We come as far as the brain and 

 distinct eyes of the lamprey. With such excellent material 

 to work upon in the lower organism, and millions of years 

 to work in, who will say that natural selection could not 

 have produced them ? And from the lowest fishes, in which 

 the brain begins to differentiate into its five parts or vesicles, 

 we trace a gradual growth without difficulty right up to the 

 ape. We know to-day that intelligence is connected chiefly 

 with the second vesicle. In the fishes and amphibians 

 natural selection developes chiefly the third vesicle ; and they 

 exhibit a limited intelligence. In the reptiles and birds it 

 developes the first vesicle ; and there are corresponding limits 

 to their mental development. In the mammals it developes 

 the second vesicle, the cerebrum ; and the higher mind 

 begins to appear. In the opossum the convolutions 

 commence, showing the growth of the cerebral matter. 

 They increase in complexity right up to the orang. The 

 psychic life advances in exactly the same proportion. 

 Which is the more rational and scientific : to say that this 

 advancing intelligence is the function of the brain, improving 

 as the organ improves, or to say that at some point or other 



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