182 ACTINOZOA. 



Of the duration of life among the Actinozoa, 

 as among Cceleiiterata in general, we are still very 

 ignorant. Some Ctenophora appear to last but a 

 single season, yet this statement can by no means 

 be regarded as true of the entire group. The 

 Alcyonaria and Zoantliaria seem long-lived and 

 hardy animals, a specimen of the common Sea- 

 anemone, kept in confinement for forty years, 

 showing no visible signs of decrepitude or old 

 age. 



In reparative power the members of this class, 

 notwithstanding their increased differentiation of 

 tissue, appear fully to rival the Hydrozoa. Many 

 experiments show how complete may be the healing 

 of wounds and regeneration of lost parts among a 

 large number of Actinozoa. Occasionally the pro- 

 cess of reparation displays itself in a curiously 

 abnormal manner. Thus, a section having been 

 made below the disc of a Sea-anemone, tentacles 

 were developed from both of the fresh surfaces 

 thus exposed. 



A common British Zoantharian, Anthea cereus, 

 adapts itself well to the conditions of such experi- 

 ments. Artificial fission of this species, if per- 

 formed with care, does not always result in death 

 of the parts so divided. 



The same animal may also illustrate the mode 

 in which spontaneous fission occurs among many 

 other forms of Actinozoa. A longitudinal cleavage 

 of the polype commences, in most cases, across 

 the region of the disc, and thence proceeds down- 

 wards towards its proximal extremity. 



Less frequently is fission effected by the separa- 

 tion of small portions from the attached base of 

 the primitive organism, whose form and structure 



