56 



CORALS AND CORAL LSLANDS. 



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. 



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 is a 

 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, 







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e^™^ 



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 Astrasa 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 



