ANTHOZOA 75 



of their parts. In a typical form, such as the common 

 sea-anemone or a simple coral (fig. 22), the body has a 

 more or less cylindrical shape, and is attached by one 

 end, the other having an opening, the mouth (fig. 22, 2), 

 surrounded by tentacles (l). The mouth leads into the 

 oesophageal tube or stomodceum (3), which opens at its 

 lower end into the coelenteron. The latter is divided into 

 chambers by radiating partitions, the mesenteries (fig. 22, 4 

 and fig. 23 a — c), each of which consists of a thin gelatinous 

 layer in the middle and a layer of endoderm on each side. 

 In the upper part of the polyp the inner edges of the 

 principal mesenteries join the stomodseum, but in the 

 lower part they remain free, and a section in the former 

 region (fig. 23) will show the body wall and also the 

 stomodaBum, but in the latter the body wall only. The 

 tentacles (fig. 22, 1) are placed immediately above the 

 intermesenteric chambers, and the space in each tentacle 

 is continuous with that of the chamber below. A bilateral 

 symmetry is indicated by the oval or slit-like mouth, and 

 the similarly compressed stomodaBum ; also by the arrange- 

 ment of the longitudinal muscles which occur on one face 

 of each mesentery, extending from the base of the polyp 

 upwards (fig. 23). The sea-anemones have no hard parts, 

 but the majority of Anthozoa possess a skeleton, which 

 in many cases is quite external to the body, and is formed 

 of carbonate of lime (fig. 22, 8, 9) ; in others it is internal 

 and may consist of calcareous spicules, or of an axial rod 

 of horny or calcareous material. The Anthozoa are divided 

 into two Orders, (1) the Zoantharia, (2) the Alcyonaria. 



