OF COENOPSAMMIA FROM LIFU. 379 



Fig. 10. Later stage tlian Fig. 'J. The young nematocyst decreases in size and becomes 

 coarsely granular, the granules arranging themselves in a spiral line close under the external 

 membrane. The nematocyst drawn has been cut rather obliquely so that in the upper half 

 the granules of the lower side are seen, and in the lower half those of the upper side, the 

 granules in the centre appearing to be almost irregularly arranged. A comparison with 

 Fig. 7 will make this clear. 



Fig. U. Transverse section through the stouiodoeum sliowing the attachment of three 

 mesenteries. The epithelium of the stomodoeum is very thick — being formed apparently of 

 cells of an elongate columnar faoies — and opposite to the attachments of tlie mesenteries 

 crowded with goblet-like vacuoles. 



Fig. 12. Transverse section through a primary mesenterial filament immediately before 

 its convolutions commence. The structureless membrane ends in a T-shaped expansion in 

 the filament, which is well marked ofi" from the general endoderm of the mesentery. It is 

 distinctly divided into three parts, a central, crowded with goblet vacuoles, and two lateral, 

 crowded with homogeneously staining oval nuclei. A single nematocyst is seen in the central 

 part, but the nematocysts do not become numerous until its lower half is reached. 



Fig. 13. Transverse section of the same filament as in Fig. 12 in its lower third. The 

 filament is as distinctly marked off from the endoderm of the mesentery below it, but it is 

 no longer divisible into three parts, being crowded with nematocysts in different stages of 

 development — one with the thread extruded and cut off short. 



Figs. 14 — 19. Mesenterial nematocysts. (Oc. 4, oil immersion xV ** f-) 

 Fig. 14. A ripe nematocyst. The thread ends below in a mass of granules at the base 

 of the cell while the opposite end appears to lie freely in an eversible sheath, marked by 

 fine lines due to a spiral row of fine hairs. (Somewhat diagrammatical.) 



Fig. 15. Nematocyst with part of the completely ejected thread. The thread seems to 

 be extruded first and to carry behind it its eversible base, which is surrounded by a distinct 

 row of spiral hairs. At the upper end of the nematocyst, round the eversible base of 

 the thread, is a distinct depression. 



Fig. 16. Nematocyst with ejected thread, whicii is still however visible in the middle of 

 the basal portion. In the body of the nematocyst traces of a spiral sheath can be seen, from 

 which the thread seems to have been ejected. 



Fig. 17. Nematocyst with eversible base but without any appearance of a thread in 

 the cell. Near the base is a nucleus with nucleolus (both seen very rarely) and the cell 

 terminates in a nucleated peduncle, which bi-anches out over the structureless membrane. 



Fig. 18. Nematocyst possibly in an earlier stage to Fig. 17, without any distinct base 

 for the thread and with a distinct nucleus and nucleolus. 



Fig. 19. Nematocyst of a later stage to Fig. 17, with a differentiation of the protoplasm 

 into a dark spiral band, which will subsequently become the thread, lying in a clearer areji. 



Fig. 20. Section through the base of one of the dividing walls of one of tlie coenosarcal 

 canals showing the attachment of the structureless membrane to the corallum. The foi-nier 

 is drawn out into long striated bands, swelling out at their ends where they are attached 

 to the corallum. The striations appear in some cases to be due to fibres in the structureless 

 membrane, but they are not generally so well marked as in this section. The spaces between 

 the bands are completely filled by the calicoblast ectoderm. 



