CONTENTS. 



Tage. 



1. Introduction 83 



2. Historical sketch 84 



3. Distribution and habits 84 



4. Physiological notes 85 



5. Early stages 87 



6. Stage "A." Origin of the anterior enterocceles 87 



7. Stage "I',." Origin of the hydrocele 88 



8. Stage "C." Closing of the blastopore and formation of the mouth 89 



9. Stage "D." Rotation of the hydrocele completed 90 



10. Stage "E." Second pair tentacles formed 92 



11. Stage "F." Invagination of the nervous system 94 



12. Stage "G." Degeneration in the larval organ begun 95 



13 - Stage "H." Formation of subneural sinus : 96 



14. Relation of the larva to adult 96 



15. Larva of Antedon rosacea and Ophiura brevispina compared 98 



16. Literature cited 98 



17. Description of figures 99 



81 



