THE ANTHOZOA 



may show a fibrillar structure, which, in many cases, is undoubtedly 

 an artifact. It may be homogeneous and devoid of all trace of 

 structure, or it may contain numerous cells, which are either 

 branched, nucleated, so-called connective tissue cells ; nerve cells 

 and fibres, muscular fibres, or cells in which calcareous skeletal 



FIG. I. 



1. Diagrammatic longitudinal section through a typical Anthozoan zooid. w, body wall ; 

 ps, peristome ; 6, base ; t, tentacles ; st, stomodaeum ; m, mesentery. 



2. Diagrammatic transverse section through a typical Anthozoan zooid in the region of the 

 stomodaeum. ec, ectoderm ; en, endoderm ; mg, mesogloea ; sc, sulcus ; si, sulculus. 



3a. Nematocyst of Corynactis viridis, fully everted. 3b. The same, before eversion. 3c. 

 The same, partly evejted. 



4. Section through a typical Anthozoan mesentery with its mesenterial filament, en, 

 endoderm ; mg, mesogloea ; msc, muscle banner with supporting plications of the mesogloea. 



5. Portion of the muscular layer of A-nemonia sulcata showing the nerve plexus and ganglion 

 cells. (1-4 original ; 5 after O. and R. Hertwig.) 



spicules are developed. All these cells or cell-products are in- 

 trusive, and are derived from one or other of the two primary 

 limiting layers comparatively late in life. There is no third 

 embryonic layer or mesoblast in the Coelentera, and for this 

 reason, the terms mesoblast and mesoderm being synonymous, their 

 middle layer is called the mesogloea, whether it be structureless 



