CORALS AND CORAL MAKERS. ii 



occasionally persistent in the adult state. There are six pairs 

 in the first series ; six in the second ; twelve in the third ; 

 twenty-four in the fourth ; forty-eight in the fifth, and so on. 



The compartment between the two septa of each pair opens 

 at top into the interior of a tentacle, and thus tlie cavity in each 

 tentacle has its special corresponding compartment below. 

 This tentacular compartment is properly, as first recognized by 

 Prof. Verrill, the a?nbulacral, since each corresponds in position 

 and function to an ambulacral or tentacle-bearing section in the 

 Echinoderms and other Radiate animals. 



Although polyps are true Radiates, they have something ot 

 the antero-posterior (or head-and-tail) polarity, with also the 

 right-and-left, which is eminently characteristic of the animal 

 type. This is manifested in the occurrence in some polyps of 

 a ray on the disk different in colour from the general surface ; 

 of one tentacle larger than the others, and sometimes peculiar 

 in colour ; of two opposite septa in a calicle or polyp-cell larger 

 than the others, and sometimes meeting so as to divide the cell 

 into halves. The first of these marks the author has observed 

 in a Zoanthid, as mentioned in his Report on Zoophytes at 

 page 419, and represented on plate 30 : and the last is very 

 strongly developed in the cells of many Pocillopor^ (ib. p. 523)- 

 Gosse and many other authors have drawn attention to the one 

 large tentacle, and the fact that it lies in the direction of the 

 line of the mouth. Prof H. James Clark, in his "Mmd in 

 Nature," states that the order in which the fleshy septa and the 

 tentacles in an Actinia are developed has direct reference to the 

 right and left sides of the body, and that there is only one 

 plane in which the body can be divided into two halves, and 

 this is that corresponding with the longer diameter of the stom- 

 ach, or the direction of the mouth. Mr. A. Agassiz has shown 

 that in Actiniae of the genus Arachnactis, the new septa and 

 tentacles are developed on either side of the one chief or anterior 

 tentacle : and Prof. Verrill, that in Zoanthids they are formed 

 principally on either side of this anterior tentacle and also ot 

 the opposite or posterior one, and much less rapidly, if at all, 

 along the sides intermediate. This chief-tentacle marks properly 



