56 CORALS AND CORAL ISLANDS. 
Gemmipores, and some foliaceous Madrepores. Where there is 
superior budding, and sometimes in the case of inferior, the 
new polyps appear some distance from the edge, the growing 
margin spreading on in advance of the buds that open in it, 
as in the Echinopores, the Phyllastreea represented on Plate I. 
(frontispiece), and also in the Merulina of Plate VI., figure 1 
(facing page 82). 
Besides the method of budding explained in the above re- 
marks, there is also a kind of superior budding called sponta- 
neous fission, which consists in a spontaneous subdivision of a 
polyp, by which two are made out of one. In such cases the 
disk of the polyp has not a distinct limit of growth, as in the 
above, but tends to enlarge indefinitely ; and when there isa 
beginning of an increase beyond the proper adult size, a new 
mouth opens in the disk, a short distance from the old one, and 
at the same time its edges extend downward and make a new 
stomach beneath it; finally tentacles are developed between 
the two mouths, and then each polyp separates with its part of 
the old tentacles as illustrated in the following figure. It is not, 

SPONTANEOUS FISSION IN POLYPS. 
as is seen, a subdivision strictly into halves, as one carries off 
the old mouth and stomach. ‘The figure to the left represents 
a polyp of the Astra tribe, with already two mouths, through 
a commencement of the process of subdivision. In the next 
figure there are tentacles between the two mouths, so that each 
