3472 



CCELENTERA TES 



mouth, the cilia disappear, and after the mouth tube (/>) has been formed by the 

 folding in of the anterior end along the longitudinal axis of the body (L, o, a}, and 

 has thus become marked off from the stomach (g), the eight hollow tentacles 

 rise round the mouth as outgrowths of the body cavity, or as direct continuations 

 of the stomach. Like all other corals, Monoxenia periodically multiplies by means 

 of eggs which arise either in the walls of the radiating stomach partitions (or septa), 

 or on their free edges, and have to be ejected through the mouth, as development 

 does not in this case take place within the digestive cavity of the parent polyp." 



g As a rule, the polyps are either male or 



female, but in stock-forming species 

 individuals of the two sexes may be 

 mixed. Hermaphrodite individuals are 

 less frequent. 



Monoxenia may be taken as the 

 simplest type of the regularly radiate 

 polyps; in all radiate animals the dif- 

 ferent organs being repeated in regular 

 rings round the central axis. Monoxenia 

 and similar animals are considered simple, 

 because the repeated organs develop simi- 

 larly and simultaneously, and are com- 

 paratively few in number. The mouth, 

 too, is circular. In many other polyps, 

 however, the regularly radiate type 

 is slightly departed from; the mouth, 

 instead of being round, forming a long 

 slit, while there is a tendency for the 

 originally radiate animal to become 

 bilateral. From this account of a simple 

 polyp, it is easy to understand what 

 kind of animal it is which makes 

 coral; and our readers, if they have not 

 already done so, will give up speaking of 

 ' ' insects building up the coral reefs. ' ' 

 It is, however, by no means all such 

 polyps that form coral, nor do those 

 which form it produce it always in the 

 same way. Numbers of polyps, such as 

 the beautiful sea anemones, never produce 

 any hard substance, but remain soft and 

 delicate, though dangerous, at least to 

 small animals, because of their stinging 

 cells. Many of these soft sea anemones 

 are highly specialized creatures, as may 

 be seen from the colored plate; but those 



Monoxenia darwini (magnified). 



L. longitudinal section, on the left, through one of the 

 interseptal cavities, on the right, through one of the 

 partition walls ; M. Transverse section through the 

 line m n; N. Transverse section through the line 

 s b t ; O. The eight-lipped mouth aperture, with the 

 bases of the arms ; a b c o. Principal axis ; p. 

 Pharyngeal cavity ; g. Digestive cavity ; k. Divisions 

 of the digestive cavity ; iv . Radial septa or walls 

 dividing up the digestive cavity ; e. Masses of eggs ; 

 u. Mesenterial filaments ; f. Masses of muscle and 

 connective tissue. 



