REPORT ON CORALS — EXPLANATION OF PLATES. 229 



Fig. 3. View of a group of zooids as seen in the contracted condition. One gastrozooid 

 and three of the surrounding dactylozooids are shown. The gastrozooid here 

 has five tentacles. The surface of the decalcified coral is here represented 

 as seen when viewed from above, with the microscope focused somewhat into 

 the depths of the structure, A deep focus is necessary in order to reach the 

 far-retracted zooids. The deeper reticulations of the ccenosarc are thus 

 brought into view. 



M Z. Gastrozooid. 



Z, Z. Dactylozooids. 

 Fig. 4. View of the inferior surface of the superficial living lamina, from a specimen 

 decalcified in chromic acid and viewed by reflected light. The figure shows 

 the ramifications of the canals and vessels of the ccenosarc and their connec- 

 tions with the zooids of one complete group or system. 



G Z. Under surface of gastrozooid. 



D Z. One of the seven surrounding dactylozooids. 



C. Canal. 



B, B. Branches of this canaL 



B', B'. Secondary branches, from which and from B B arises a compli- 

 cated network of finer vessels. 

 Fig. 5. Enlarged view of a tentacle of a dactylozooid. 



K. Spherical head of the tentacle filled with thread-cells of various 

 sizes. 



E. Ectodermal layer. 



R C. Ramified cells or nuclei of the endodermal layer. 



M. Membranous layer. 



P. Pigmented cells within the cavity of the tentacle. 



C. Body cavity continuous with that of the. tentacle. 



Fig. 6. Diagram showing the arrangement of the muscular fibres in a gastrozooid. 

 The longitudinal muscles are gathered into bundles, which pass outwards 

 for insertion on to the radially disposed vessels of the ccenosarc. Other fibres, 

 less densely placed, occupy the interspaces between these bundles. 

 0. Mouth of the gastrozooid 



A, A. Radially disposed vascular offsets from the base of the gastrozooid. 

 L M. Longitudinal muscular bundles. 

 C M. Circular muscular fibres. 

 Fig. 7. Transverse section of a gastrozooid. 



E. Ectodermal layer, containing thread-cells in various stages of develop- 

 ment. 

 M. Membranous layer. 



O' 



