34 THE ORIGIN OF VERTEBRATES 



Amphioxus, like the tunicates, does not possess the character- 

 istics of other vertebrates. In all vertebrates above these forms 

 the great characteristic is a well-defined brain-region from which 

 arise nerves to organs of special sense, the eyes and nose. la 

 Amphioxus no eyes exist, for the pigmented spot at the anterior 

 extremity of the brain-region is no eye but only a mass of pig- 

 ment, and the so-called olfactory pit is a very rudimentary and 

 inferior organ of smell. In connection with the nearly complete 

 absence of these two most important sense-organs, the most im- 

 portant part of the central nervous system, the region corresponding 

 to the cerebral hemispheres, is also nearly completely absent. 



Now, the history of the evolution of the central nervous system in 

 the animal race points directly to its formation as a concentrated 

 mass of nervous material at the anterior extremity of the body, in 

 consequence of the formation of special olfactory and visual organs 

 at that extremity. As already stated, the concentration of nervous 

 material around the mouth as an oral ring was its beginning. In 

 connection with this there arose special sense-organs for the guidance 

 of the animal to its food which took the form of olfactory and optic 

 organs. With the shifting from the radial to the elongated form 

 these sense-organs remained at the anterior or mouth-end of the 

 animal, and owing to their immense importance in the struggle for 

 existence, that part of the central nervous system with which they 

 were connected developed more than any other part, became the 

 leader to which the rest of the nervous system was subservient, and 

 from that time onwards the development of the brain-region was 

 inevitably associated with the upward progress of animal life. 



To those who believe in Evolution and the Darwinian theory of 

 the survival of the fittest, it is simply inconceivable that a soft-bodied 

 animal living in the mud, blind, with a rudimentary brain and rudi- 

 mentary olfactory organs, such as is postulated when we think of 

 Balanoglossus and Amphioxus, should hold its own and come victorious 

 out of the struggle for existence at a time when the sea was peopled 

 with powerful predaceous scorpion- and crab-like armour-plated 

 animals possessing a well-developed brain, good eyes and olfactory 

 organs, and powerful means of locomotion. Wherever in the scale of 

 animal development Amphioxus may ultimately be placed, it cannot 

 be looked upon as the type of the earliest formed fishes such as 

 appeared in Silurian times. 



