

ACTINOZOA 



183 



a 



m 





they subsequently, by gradual development, tend 



to assume. 



Further observations are wanting on the occur- 

 rence of fission and gemmation among the Cteno- 

 pjiora. In none of these animals do we find 

 colonies of zooids resulting, as in the Hydrozoa, 

 from a process of continuous budding. 



But in other Actinozoa continuous gemmation 

 abundantly takes place, and in this manner are 

 formed those composite structures, consisting of 

 numerous polypes, met with among so many 

 genera of Zoantharia, Alcyonaria and Rugosa. 

 In a few of these organisms, discontinuous gem- 



mation may also be noticed. 



) 



the sides of the polypes, or (3) from their oral 

 discs. Since these surfaces are but parts of a 

 common integument it might be anticipated that 

 intermediate positions of buds would now and 

 then occur. Nevertheless, it has been found con- 

 venient to distinguish three principal modes in 

 which gemmation of polypes may be effected, as 



the basal, the 'parietal, and the calicular, respec- 

 tively. 



In basal gemmation the polype sends forth a 

 rudimentary coenosarc, from which, after a time, 

 the young polype-bud is produced, and so on for 

 all the zooid forms subsequently evolved. 



The extent to which a coenosarc may be deve- 

 loped varies, however, considerably. It must not 

 he inferred that in every composite Actinozoon 

 such a structure is present ; for the mass may 

 exhibit nought else save a congeries of polypes 

 m immediate mutual connection. In this case 



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