66 ZOOLOGY 
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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 
Fic. 45.—A mesentery of Tealia 
crassicornis. After the Hertwigs. 
. Edge of mouth. 
2. External and internal pores in the 
mesentery. 
. Mesenterial filament. 
. Testis follicles, 
5. Cireular muscle. 
. Radial muscle fibres. 
. Longitudinal muscle fibres. 
. Parietal longitudinal muscle fibres. 
. Lower edge of the stomodaeum. 
intramesenterie 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 
