50 GILBERT 0. BOURNE. 



EXPLANATION OF PLATES III & IV. 



Illustrating Mr. G. C. Bourne's paper " On the Anatomy of 

 Mussa and Euphyllia, and the Morphology of the Madre- 

 porarian Skeleton." 



Fig. 1. — Portion of a colony of Mussa corymbosa,of which the polyps 

 are retracted and shrunk by the action of alcohol. Half natural size. r. Limit 

 of soft tissues external to the corallum. (Randplatte of von Heider.) 



Fig. 2. — Transverse section of the calyx of Mussa corymbosa, showing 

 two principal and one secondary septum. The dark lines or areas are centres 

 of calcification, and around them are concentric lines of growth. •$. s. Sutures. 

 d. Dissepiments. 



Fig. 3. — Transverse section across a single polyp of Mussa corymbosa, 

 to show the arrangement of the septa and dissepiments. The corallum is 

 represented in white and the soft tissues in black. The spaces between the 

 dissepiments and the theca not occupied by any soft tissues are shaded, th. 

 Theca. sp 1 . Principal septa, sp" 1 . Secondary septa, d. Dissepiments, r. 

 Randplatte. 



Fig. 4. — Diagram of a longitudinal section through Mussa corymbosa. 

 On the right side the section passes close to one of the principal septa. On 

 the left side a mesentery is exposed. The mesoglcea is represented in black, 

 the ectoderm shaded with vertical lines, st. Stomodseum. ec. Ectoderm. 

 nig. Mesoglcea. en. Endoderm. cy. Calicoblast layer, mf. Mesenterial fila- 

 ments, m. Mesentery, with longitudinal muscles, r. Randplatte. d. Dis- 

 sepiments. 



Fig. 5. — Part of a transverse section through the hard and soft parts of 

 Mussa corymbosa, just below the level of the stomodeeum. The section 

 comprises one of the ends of the long axis of the polyp. Mesogloea, ectoderm, 

 and endoderm shaded as in Fig. 4. m'. Extrathecal portions of the mesen- 

 teries, mc. Pleats of mesogloea, to which the mesenterial muscles are 

 attached. Remainder of the lettering as in Fig. 4. 



Fig. 6. — Euphyllia glabrescens, natural size, showing the expanded 

 polyp and the extension of the Randplatte over the lip of the calyx. At x 

 the Randplatten of adjacent polyps are seen to be continuous, forming a 

 ccenosarc. r. Limit of the Randplatte. 



Fig. 7. — Transverse section through the calyx of Euphyllia glabrescens, 

 showing primary (sp 1 .), secondary (sp".), and tertiary (sp 3 .) septa. The centres 

 of calcification are shown by dark lines, s. s. Sutures, d. Dissepiments. 



