ANATOMY OF MUSSA AND EUPHYLLIA. 51 



Fig. 8. — Part of a transverse section through a decalcified polyp of 

 Euphyllia glabrescens. This section shows the Randplatte r, including 

 the extrathecal ccelenteron and the extrathecal portions of the mesenteries* 

 m'. The endoderm, en'., of the intrathecal part of the polyp is greatly vacuo- 

 lated, forming a reticular tissue, which fills up the whole of the ccelenteron and 

 contains in its meshes zooxanthellse and nematocysts. The stomodseal canals, 

 st. c, occupy the axial part of the polyp, and serve as the digestive cavity. 

 ov. Ova. n. c. Nutritive cells. 



Fig. 9. — Developing nematocyst from the stomodseum of Euphyllia 

 glabrescens. Magnified 750. 



Fig. 10.— Ripe nematocyst from the stomodseum of Euphyllia glabres- 

 cens, with the axis tube everted, but the thread not ejected. Magnified 750. 



Fig. 11. — A nematocyst similar to that in Fig. 10, but with the thread only 

 ejected, showing the armature at the tip of the latter. 



Fig. 12. — A nematocyst from the endoderm of Euphyllia glabrescens. 



Fig. 13. — Longitudinal section through an Astroides embryo, copied from 

 von Koch, showing the basal plate, bp., being formed from the ectoderm 

 (calicoblast layer) of the base of the polyp, and a septum, sp., in the process 

 of formation. The epitheca, ep., is seen at the base of the polyp, z. The 

 piece of cork on which the embryo rests. 



Fig. 14. — Diagram to exhibit the relations of the polyp to the corallum. 

 T. T. Tentacles, ec. Ectoderm, mg. Mesoglcea. en. Endoderm. si. Stomo- 

 dseum. mf. Mesenterial filaments, r. Randplatte. m. Mesentery, m'. Ex- 

 trathecal portion of mesentery, th. Theca. Bp. Basal plate, ep. Epitheca. 



Fig. 15. — Diagram to exhibit the formation of the theca from the fused 

 peripheral ends of the septa, cm. Columella. Remainder of the lettering as 

 in Fig. 14. 



Fig. 16. — Section across the calyx of Astrea cavernosa, showing 

 alternately larger (sp 1 .) and smaller (sp-.) septa. In each septum can be seen 

 the dark centres of growth and the sutures, s., marking off contiguous septa 

 from one another, t. th. Intercalated pieces lying between the ends of the 

 septa (true thecal pieces ?). 



Fig. 17. — Mussa distans. In this specimen the corallites may in some 

 instances be seen standing apart, in which case their lower portions are covered 

 by a loose epitheca, ep. In other places the corallites are set closer together, 

 and the valleys between them are partially filled up by a loose epitheca. In, 

 yet other places the calices are completely soldered together by epitheca, cos. 

 which fills up the valleys to the lips of the calices, and has the same functions 

 and relations as ccenenchyme. 



