CONTENTS. 



Pago. 



Introductory note by Prof. W. K. Brooks 72 



Introduction 75 



Methods 76 



Breeding habits 715 



Laying of eggs 77 



Fertilization 77 



Segmentation 77 



Gastrulation and further changes in the form of the larva 79 



Formation of the mesoderm 80 



Further growth of the young larva 82 



General account 82 



Nephridial pit 84 



-Medullary plate 84 



Trunk cavity 84 



Fully developed Actinotrocha 85 



Species A 86 



Species B 86 



Internal organization of the fully developed Actinotrocha 87 



Subneural gland 87 



Oral and atrial grooves 87 



Neuropore _ 88 



Subneural sinus 88 



Stomach diverticula 88 



Notochords 88 



Nervous system 89 



Muscular system 92 



Body cavities, mesenteries, etc 93 



Nephridia 95 



Rudiments of the adult blood vessels in the Actinotrocha 96 



Blood corpuscles and their origin 97 



Rudiment of the "adult collar cavity" _ 98 



Metamorphosis 98 



Preoral lobe and tentacles 99 



Ganglion 99 



Ectodermal wall of collar 99 



Perianal ciliated ring and ectodermal wall of the trunk 99 



Cavity of the preoral lobe 99 



Mesentery between the lobe and collar 99 



Larval collar cavity 99 



Adult collar cavity 100 



Trunk cavity and cavity of the ventral pouch 100 



Ventral and lateral mesenteries 100 



Stomach diverticula 100 



Digestive areas 1 00 



Nephridia 100 



Vascular system 101 



Adult Phoronis architi eta 102 



( ieneral account 102 



Lophophoral organs 103 



Vascular system 105 



Nervous system 106 



Nephridia 107 



Reproductive organs 107 



Ciliated ridge of the alimentary canal 107 



Summary 107 



References Ill 



73 



