CONTENTS XXI 



Page 



14. The Sense Organs 5^3 



Evolution and Development of Sense Cells 5^3 



Evolution and Development of Cutaneous Senses 5^6 



Evolution and Development of Lateral Line Organs 568 



Evolution and Development of Muscle Spindles 57i 



Evolution and Development of Olfactory Organs S7i 



Evolution and Development of Taste Organs 577 



Evolution and Development of Visual Organs S^o 



Evolution and Development of Static and Auditory Organs 594 



15. The Head Problem 607 



Transcendental Phase 6°7 



Anatomical Phase ^°9 



Embryological Phase "^° 



Summary of the Evidence ^26 



16. The Ancestry of the Vertebrates 628 



Annelid Theory ^3° 



Delsman's Theory "3" 



The Arthropod Theory 642 



Gaskell's Arachnid Hypothesis 643 



Patten's Arachnid Hypothesis 652 



The Nemertean Hypothesis "57 



The Balanoglossus Theory ^59 



Appendicularia Theory ""^ 



Conclusion ^^'^ 



Glossary ^^7 



Index 691 



