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. In 
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. 
