262 THE BIOLOGY OF THE SEA-SHORE 



Anthozoa. — Though a good many anemones may repro- 

 duce asexually by a process of fission, e.g. Metridium {Actino- 

 loba), the sexual method is more common. In some 

 anemones a curious form of asexual reproduction occurs 

 known as " pedal laceration." In the common British 

 Metridium, for instance, a favourite aquarium species, " the 

 pedal disc sometimes spreads on the glass or rock upon 

 which the animal rests, in the form of a thin membrane or 

 film of an irregular circular shape, nearly twice the diameter 

 of the column. As the anemone glides along, the film 

 remains behind and breaks up into a number of hemispherical 

 droplets, which in a few days develop tentacles, a mouth, 

 mesenteries, and other organs of a complete independent 

 anemone. A similar method of reproduction has been 

 observed in several species of Sagartia." (Hickson, op. cit.) 

 As in the case of most sessile anim*als, anemones are 

 hermaphrodite forms and fertilisation may take place either 

 externally {Actinoloba marginata, A. dianthus, Sagartia sps. 

 Actinia cari, Anemonia sulcata, Calliactis parasitica) or 

 internally {Bunodes sps. Cereactis aurantiaca, Sagartia troglo- 

 dytes, Bunodactis gemmacea, etc.). Where fertilisation takes 

 place in the water the early larvae are oval or pear-shaped 

 and covered with cilia. Their further development depends 

 on their finding a suitable place for fixation within a 

 comparatively short time. Where fertilisation takes place 

 internally the embryos are sometimes retained within the 

 body cavity of the parent to an advanced stage, the length 

 of time depending upon the risks to which the young are 

 likely to be exposed. Thus, in Arctic species, the embryos 

 are retained within the body until several cycles of tentacles 

 are developed or even the full complement. The common 

 British species. Actinia equina, also liberates what are practi- 

 cally young adults, though the incubation period is said not 

 to be so prolonged as in the same species in the tropics. 



The gonads of British species usually ripen in spring or 

 summer ; but aquarium specimens, if regularly fed, will 

 reproduce all the year round. 



Anemones are an unusually long-lived group, at least 



