126 CCELENTERATA OR STINGING-ANIMALS. 



General Classification. 



The Coelenterata are often classified as follows : — 



, Craspedota. Hydridse, e.g. Hydra ; Hydiomeduste 

 \ ( Hydroid colonies, often with free medusoids) ; 



A. Hydrozoa. \ Trachymedusse (permanent medusoids) ; Si- 



/ phonophorse (free colonies of medusoids. 



^ Acraspeda. True jellyfishes, e.e- Aurelia, Cyanea. 



( Alcyonaria,?.^.^/g'o««"«(Dead-men's- ) and 



B. Actinozoa. \ fingers.) \ related^ 



( Zoantharia, e.g. Actinia (Sea-anemone.) ) "corals/ ' 

 C' Ctenophora, e.g. Beroe and Cestum Veneris (\'enus' Girdle). 



I prefer the following arrangement suggested by other authorities : — 



A. Class Hydrozoa. Orders Hydridx, HydromedusiE, Siphono- 

 phora:. 



B. Class Scyphozoa. Sub-classes, Scyphomedusie or Acraspeda ; 

 and Anthozoa or Actinozoa. 



C. Class Ctenophora. 



Survey of Types. 



I I. Order Hydridse, 

 A. The Class Hydrozoa — ^ 2. Order Hydromedusse. '' 



( 3. Order Siphonophorae. 



Illustrated (i) by Hydra. 



General Life. — Various species of Hydra, especially the 

 green H. viridis and the brown H. fusca, occur abundantly 

 in fresh-water ponds. They are simple tubular animals with 

 a crown of tentacles around the mouth. Large well extended 

 specimens may measure one half to three-quarters of an inch 

 in length, but they are as thin as needles. They contract 

 into small knobs, which are not readily seen on the leaves of 

 the duck-weed or other water plants, from the under surface 

 of which they hang The animal sways its body and tentacles 

 backwards and forwards, but does- not often move from its 

 attachment. It can indeed loosen its base, lift itself by its 

 tentacles, and stand on its head, but it evidently prefers a 

 quiet life. Its food consists of small organisms, which are 

 paralysed or killed by the stinging-cells on the tentacles, and 



