Sea Anemones. 43 



The body-cavity is lined by endoderm and extends 

 upwards into the hollow tentacles, each of which is in 

 fact a tubular prolongation continuous with this cavity. 

 In life, when the body is expanded, the space between 

 the stomach and the body wall contains sea-water 

 which also distends the tentacles, but on irritation the 

 contraction of the outer wall drives out this fluid, 

 which escapes in minute jets through the terminal 

 pores at tha extremities of the tentacles. 



The body cavity is divided by vertical partitions 

 which pass inwards to the outside of the stomach-wall, 

 and thus divide the outer chamber into a series of 

 smaller compartments which radially surround the 

 stomach, below which they all communicate with 

 each other. There are five or six such large parti- 

 tions extending the whole length of the body wall, 

 which are called primary mesenteries, and between 

 them are smaller partitions in equal numbers, called 

 secondary mesenteries, between these, there are often 

 still smaller tertiary mesenteries, twice the number of 

 the primaries, and in some related forms other orders 

 of intermediate partitions exist, still farther sub-divid- 

 ing the body cavity, but each set shorter than its pre- 

 decessors. 



The outer surface of a sea anemone, and especially 

 of the tentacles, is richly covered with thread cells, 

 which, when burst, are sometimes thrown off as a 

 continuous slough. This can be seen when an ane- 

 mone is imprisoned in a bottle of sea-water, and in 

 the same condition we notice that as the water be- 

 comes less able to support the life of the creature 

 from its loss of oxygen and of material for food, that 



