66 LIFE BY THE SEASHORE. 



the ejection of their numerous stinging-cells, which are 

 too weak to pierce the skin. When molested the anemone 



a 1 es not shrink down in the way in which the hydroid 

 Dphytes do, but contracts a circular muscle at the top of 

 B column, and pulls the tentacles inwards at the same 

 ae. The result may be compared to the closing of a bag 

 drawing a string run in its margin. The mouth is a 

 longitudinal slit, whose walls are much grooved. Of the 

 grooves two are more distinct than the others, and con- 

 stitute the " siphonoglyphes." which are structures of 

 considerable interest to the student of form. It is not 

 easy to get a practical notion of the internal anatomy 

 of a sea-anemone without subjecting it to special treat- 

 ment; but sometimes some of the more transparent 

 species can be studied in the living condition by holding 

 expanded specimens in a glass jar up to the light. The 

 more important points may be briefly summarised as follows. 

 The mouth opens into a short gullet, which itself opens 

 into the general cavity ; this gullet can be clearly seen when, 

 as often happens, captive anemones partially turn themselves 

 inside out, and is produced by an infolding of the body-wall. 

 The gullet does not hang freely in the general cavity, for a 

 number of partitions or mesenteries run from it to the 

 body-wall, so that a cross-section of the upper part of a 

 sea-anemone would show a central chamber surrounded by 

 radial chambers. These radial chambers are traversed by 

 other narrow mesenteries which project from the body-wall, 

 but do not extend inwards so far as the gullet. On the 

 mesenteries are borne the reproductive organs, and also 

 certain tangled threads, supposed to be of importance in 

 digestion. These are often seen when an anemone is 

 ruptured in the attempt to remove it from a rock surface. 

 In certain anemones, but not in the smooth anemone, 

 the mesenteries also bear long, slender threads, crowded 

 with stinging-cells, and capable of being shot out by 

 pores in the body-wall. In Actinia these acontia seem 

 to be functionally replaced by the " batteries of stinging- 

 cells," which form the row of blue beads visible at the 

 base of the tentacles. The chief points of contrast 

 between a sea-anemone and a hydroid polype are : the 

 presence in the former of a distinct gullet, of mesenteries 



