THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM 67 
compelled to pass the whole of his food through the narrow wsophageal tube, 
still existent in him as the infundibular tube. This, then, is the working 
hypothesis upon which this book is written. If this view is right, that the 
Vertebrate was formed from the Palewostracan without any reversal of surfaces, 
but by the amalgamation of the central nervous system and alimentary canal, 
then it follows that we have various fixed points of comparison in the central 
nervous systems of the two groups of animals from which to search for further 
clues. Itfurther follows that from such starting-point every organ of importance 
in the body of the arthropod ought to be visible in the corresponding position in 
the vertebrate, either as a functional or rudimentary organ. The subsequent 
chapters will deal with this detailed comparison of organs in the arthropod and 
vertebrate respectively. 
