66 



ZOOLOGY 



edge of the mesentery is free. The secondary mesenteries have 

 not reached the oesophagus in Fig. 46, so that the whole 

 extent of their inner edge is free. The mesenteries are grouped 

 in pairs, and the members of each pair are separated by an 



Fig. 45, — A mesentery of Tealta 

 crassieomis. After the Hertwigs. 



1. Edge of mouth. 



2. External and internal pores in the 



mesentery. 



3. Mesenterial filament. 

 i. Testis follicles. 



5. Circular muscle. 



6. Radial muscle fibres. 



7. Longitudinal muscle fibres. 



8. Parietal longitudinal muscle fibres. 



9. Lower edge of the stomodaeum. 



intramesenteric space, while the various pairs have an inter-septal 

 chamber between them. The secondary mesenteries always occur 

 between two primary ones. Each mesentery is pierced by a 

 round hole, and in some species by two, so that the various 

 intermesenteric chambers open into one another above, as well 

 as all communicating with the central chamber below. 



Along one side of each mesentery runs a longitudinal 

 bundle of muscle fibres from the peristome to the base. These 

 assist the sea-anemone to contract. They are as a rule facing 

 one another in each pair. But on each side of each siphono- 

 glyph is a mesentery known as the directive mesentery (Fig. 46), 

 and on these the longitudinal muscles turn away from each 

 other. Transverse muscle fibres are found on the mesenteries 

 on the side where the longitudinal muscles do not exist. There 

 are also sphincter muscles running round the peristome, and 

 parietal muscles running obliquely from the walls to the base 



