136 LEISURE-TIME STUDIES. 



by a process of fission, that is, of simple division of the 

 body-substance into new individuals. The occurrence of 

 this process in the corals is not surprising when we consider 

 that the common sea-anemone may be divided artificially, 

 like the hydra, with the result of producing one or more new 

 individuals. Some of the star corals or Astraeas, of the Pacific, 

 grow into great stony hemispheres through this method of 

 increase, these masses frequently possessing a diameter of 

 from ten to fifteen feet. Life and death in the living coral, 

 to use Mr. Dana's words, may be regarded as "going on 

 together, pari passu? As new living parts are developed, 

 the older parts die, but necessarily leave behind their coral- 

 substance to form enduring parts of the mass. In some cases, 

 according to the author just quoted, " a polyp, but a fourth 

 of an inch long, or even shorter, is finally found at the top 

 of a stem many inches in height. . . . The tissues that 

 once filled the cells of the rest of the corallum have dried 

 away, as increase went on above. . . . The coral-zoophyte 

 may be levelled by transported masses swept over it by the 

 waves; yet, like the trodden seed, it sprouts again, and 

 continues to grow and flourish as before." Thus the fertility 

 of the coral-polypes may be regarded as of double nature, 

 since we find that each member of a coral colony is capable 

 first, of giving origin to eggs, each of which when duly 

 developed represents the initiatory stage in the production of 

 a new colony; and secondly, of increasing each individual 

 colony by an unlimited process of budding or fission. 



As features in the general structure of corals, which 

 deserve a brief notice by way of conclusion to their per- 

 sonal history, we may refer to the main differences observ- 

 able in the coral-structure, and to certain variations in the 

 chemical composition of the coral. A piece of red coral, 

 or mare's-tail (Fig. 13), exemplifies one of the two chief 

 varieties of coral ; the coral-substance forming in this instance 

 a solid central axis, on the outside of which the living bark 

 consisting of numerous polypes is situated. In this and 

 similar cases, all traces of the separate coral-polypes dis- 



