MICROSCOPICAL STUDIES. 75 



arrangement can be at once understood if we take a hollow india- 

 rubber ball, cut a small slit at one end, and then push the edges of 

 the slit well down into the interior of the ball ; the short tube 

 thus formed will represent the stomodseum. 



Each of the two angles that bound the extremities of the mouth 

 slit are continued downwards along the oesophagus as a deep, richly 

 ciliated groove — the siphonoglyph. Most anemones have two of 

 these grooves but some (Peachia, Cerianthus) have but one. 



The siphonoglyphs remain open, even when the animal is 

 greatly contracted, and they appear to be useful in keeping up a 

 constant flow of water through the oesophagus. 



Numerous vertical partitions, ingrowths of the body wall — the 

 mesenteries — join the hanging oesophageal tube to the outer wall 

 of the body, and serve to break up the great body-cavity into a 

 number of radial longitudinal chambers ; an arrangement clearly 

 shown in Fig. 1, representing a transverse section through the upper 

 part of an anemone. The section of the oesophagus appears as a 

 small inner circle, connected to the large outer circle of the body 

 w r all by twelve radial lines, the sections of the mesenteries. But in 

 the lower part of the Anemone's body — below the level of the 

 oesophagus, the mesenteries form incomplete partitions, and show 

 as in Fig. 2, as though a cart wheel had had the hub broken out 

 leaving the rim with the broken spokes projecting inwards. The 

 free edge of each mesentery is swelled out distinctly into three 

 longitudinal lobes, the middle one crowded with nematocysts and 

 gland cells, the lateral ones clothed with strong cilia. 



The mesenteries are arranged in pairs. Some reach across 

 to the oesophagus — the primary ; others fall a little short of it — 

 the secondary, and yet others may be still shorter — the tertiary. 

 Of these the primary are the first to appear. The secondary appear 

 next in succession, in pairs between every two pairs of primary. In 

 Fig. 2, four pairs only of secondary mesenteries (2 m) are present, 

 while the full complement of primary, six pairs, is obvious. Each 

 mesentery has a very pronounced longitudinal ridge on one face 

 running from peristome to base (lm), and except in two pairs, the 

 ridges in each pair face one another. The two exceptional pairs are 

 on opposite sides of the oesophagus. In them, the ridges, in the 

 members of each pair, face outwards, and the presence of these 

 directive mesenteries {dm) serves to divide the animal into a right 

 and a left half, and in certain cases, even into a dorsal and a ventral 

 division. When two siphonoglyphes are present, each gives attach- 

 ment to the inner margins of one of these two pairs of special septa. 

 The chamber enclosed by the members of each pair of mesen- 

 teries is the intraseptal (im) ; that between the outer members of 



