CONTENTS. 



Page. 



1. Introduction 83 



2. Historical sketcli 84 



3. Distribiitiim :iiiil lialiits 84 



4 . Pliysiological notes 85 



5. Early stages 87 



6. Stage "A."' Origin of the anterior enterociclos 87 



7. Stage "B." Origin of the liytlrocci-le 88 



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



9. Stage •'!)." Rotation of the hydrocitle completed 90 



10. Stage "E." Second pair tentacles foimed 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 % 



1.5. Larva of Antedon rosacea and Ophiura brevisi>ina compared 98 



111. Literature cited 98 



17. Description of figures 99 



81 



