16 THE ORIGIN OF VERTEBRATES 
organ being considered by them as the great characteristic of the 
vertebrate; indeed, so much is this the case, that a large number 
of zoologists speak now of Chordata rather than of Vertebrata, and 
in order to emphasize their position follow Bateson, and speak of the 
Tunicata as Uro-chordata, of Amphioxus as Cephalo-chordata, of the 
Enteropneusta as Hemi-chordata, and even of Actinotrocha (to use 
Masterman’s term), as Diplo-chordata. 
The upholders of this theory lay no stress on the nature of the 
central nervous system in vertebrates, they are essentially zoologists 
who have made a special study of the invertebrate rather than of 
the vertebrate. 
Of these two methods of investigating the problem, it must be 
conceded that the former is more likely to give reliable results. 
By putting the vertebrate to the question in every possible way, by 
studying its anatomy and physiology, both gro3s and minute, by 
inquiring into its past history, we can reasonably hope to get a 
clue to its origin, but by no amount of investigation can we tell 
with any certainty what will be its future fate; we can only guess 
and prophesy in an uncertain and hesitating manner. So it must be 
with any theory of the origin of vertebrates, based on the study of 
one or other invertebrate group. Such theory must partake rather 
of the nature of prophecy than of deduction, and can only be placed 
on a firm basis when it so happens that the investigation of the 
vertebrate points irresistibly to its origin from the same group; in 
fact, “never prophesy unless you know.” , 
The first principle, then, I would lay down is this: In order to 
find out the origin of vertebrates, inquire, in the first place, of the 
vertebrate itself. 
IMPORTANCE OF THE CENTRAL NERVOUS SYSTEM. 
Does the history of evolution pick out any particular organ or 
group of organs as more necessary than another for upward progress ? 
If so, it is upon that organ or group of organs that special stress must 
be laid. 
Since Darwin wrote the “Origin of Species,” and laid down that 
the law of the ‘ survival of the fittest’ is the factor upon which evolu- 
tion depends, it has gradually dawned upon the scientific mind that 
‘the fittest’ may be produced in two diametrically opposite ways: 
