chap, xv Backboneless Animals 225 



which Dead -men's -fingers (Alcyonium digitatum) is a common 

 type. Animals resembling sea-anemones have often much lime 

 about them, and the same is true of others which resemble 

 Alcyonium ; in both cases we call these calcareous forms corals. 



In this bird's-eye view of Stinging-animals, we have recognised 

 the great types, but we have left others of minor importance out of 

 account, especially certain corals belonging to the hydroid series 

 and known as Millepores, also the Portuguese Man-of-War and 

 its relatives (Siphonophora), which are colonies of more or less 

 medusoid individuals with much division of labour, and lastly the 

 Ctenophores, such as Beroe and Pleurobrachia, which represent the 

 climax of activity among Ccelenterates. 



A brief recapitulation will be useful : 

 First Series — Hydroid and Medusoid types (Hydrozoa) : — 



(1) The freshwater Hydra and a few forms like it. 



(2) The hydroids or zoophytes, each of which may be regarded 



as a compound much-branched Hydra ; including (a) many 

 whose reproductive persons are not liberated, especially 

 Sertularians and Plumularians ; — (b) many whose repro- 

 ductive persons are liberated as swimming bells or 

 * medusoids, especially Tubularians and Campanularians. 



(3) Free medusoids, anatomically like the liberated bells of 2 (b), 



but without any connection with zoophytes. 



(4) A few colonial medusoids such as the Portuguese Man-of- 



War (Physalia). 



(5) A few hydroid corals or Millepores. 



Second Series — Jellyfish and Sea-Anemone types (Scyphozoa) : — 



(1) The true jellyfishes or" Medusa;, including (a) a form like 



Pelagia which is free-swimming all its life through, (b) the 

 common Aurelia whose embryos settle down and become 

 polypes from which the future free -swimming jellyfishes 

 are budded off, (c) the more or less sedentary jellyfish 

 known as Lucernarians. 



(2) The sea-anemones and their relatives, including (a) sea- 



anemones proper (e.g. Actinia) and their related reef- 

 building coral-colonies (e.g. star-corals Astrcea, brain-coral 

 Mceandrind) ; and (b) Dead-men's-fingers (Alcyonium) and 

 others like it, also with related corals, e.g. the organ-pipe 

 coral (Tubipora musica) and the "noble coral" of com- 

 merce (Corallium rubrum). 

 Third Series--^ 



The Ctenophores, which are markedly contrasted with corals, 



being free and light and active. Many (e.g. Beroe and 



Pleurobrachia) swarm in our seas in summer, iridescent in 



daylight, phosphorescent at night. They differ in many 



Q 



