184 



ACTINOZOA. 



multiplication by fission or by parietal gemma- 

 tion has probably occurred (Jig. 32). 



If parietal gemmation be repeated several times 

 during the growth of the budding organism, it is 

 said to be indefinite ; if once only, definite. 



Indefinite gemmation is termed regular when 

 the young polypes arise at points which are deter- 

 minate for the same species; irregular, when 

 buds are produced indifferently from different parts. 



The results of definite gemmation vary accord- 

 ing as the producing and produced zooids are 

 turned towards the same side, or in opposite direc- 

 tions. 



Calicular gemmation is only known anion a- cer- 

 tain extinct coralligenous Actinozoa. In Cyatho- 

 phyllum and its allies, members of the order 

 Rugosa, the primitive polype sends up from its 

 oral disc two or more similar buds, these, in their 

 turn, produce other young polypes, and thus, the 

 process is repeated, until an inverted pyramidal 

 mass of considerable size is formed, all the parts 

 of which rest upon the narrow base of the first 

 budding polype. 



Milne Edwards has carefully insisted on the 

 necessity of distinguishing between fission and 

 gemmation among the Actinozoa. The oral disc 

 of the budding polype always remains entire, and 

 the bud, when it first appears, wants not only a 

 mouth, but most of the other structures which 

 subsequently it acquires; whereas the polypes 

 produced by fission resemble each other in organ- 

 isation and, not unfrequently, in size, as soon as 



they become distinct. 



hardly 



said, oral fission is referred to; basal fission, a 

 mere variety of discontinuous gemmation, being, 



