STRUCTURE OF A SEA ANEMONE. 151 



the body wall. The tentacles are continuous with the cavi- 

 ties between the mesenteries, and thus all the parts of the 

 body are in communication. The mouth is usually a longi- 

 tudinal slit, and its two corners are often richly ciliated. The 

 gullet is marked with longitudinal grooves, two of which, the 

 " siphonoglyphes," correspond to the angles of the mouth, 

 and are especially broad and deep. Along these two grooves, 

 and by these two corners, food particles usually pass in ; but 

 in some, one side is an incurrent, the other an excurrent 

 channel. Occasionally, only one corner of the mouth and 

 side of the gullet is thus modified. The gullet often extends 

 far down into the cavity of the anemone. It admits of a 

 certain amount of extrusion. The mesenteries bear (a) 



FIG. 47. Section through Sea anemone (across arrow in 

 Figure 46). (After ANDRES.) 



A. B., directive septa; m.f., mesenteric filaments; g, genital 

 organs ; m.L, longitudinal muscles ; s, primary septum ; s', second- 

 ary septa ; s", tertiary septum. The arrow enters between two 

 primary septa (an intra-septal cavity) and passes out between two 

 tertiary septa. 



mesenteric filaments ; (/>) retractor muscles ; (c) ridges of 

 reproductive cells, almost always either ova or spermatozoa, 

 rarely both ; and (d) in some cases offensive threads 

 (acontia), rich in stinging cells, and extrusible through the 

 body wall. The mesenteric filaments seem to be closely 

 applied to the food and perhaps secrete digestive juice. 

 Intracellular digestion also occurs. Sea anemones have no 

 sense organs ; the sapphire beads, which are so well seen at 



