CONTENTS ix 



CHAPTER XV 

 Final Remarks 



PAGE 



Problems requiring investigation — ■ 



Giant nerve-cells and giant nerve-fibres ; tbeir comparison in fisbes and 

 artbropods ; blood- and lymph-corpuscles ; nature of the skin ; origin of 

 system of unstriped muscles ; origin of the sympathetic nervous system ; 

 biological test of relationship. 



Criticisms of Balanoglossus theory — Theory of parallel development — Importance 



of the theory advocated in this book for all problems of Evolution . . 488 



Bibliography and Index of Authors 501 



General Index 517 



