50 INVERTEBRATE AXIMALS. 



SUB-KINGDOM II. CCELENTERATA. 



CHAPTER V. 



1. Characters of the Sub-Kixgdom. 2. Divisions. 



.3. General Characters of the Hydrozoa. 



4. Explanation of Technical Terms. 



The second great jiriniary division or sub-kingdom of animals is 

 tb:it of tlie Vcelenteruta or " bollow-entrailed " anim.als (Gr. knilos, 

 liullow ; enterciii, intestine). Tbis sub-kingdom embraces tbe Sea- 

 anemones, Corals, Sea-jellies, Sea-tirs, Sea-pens, and otber allied 

 animals, all of -ndiicb are cbaracterised, amongst other tilings, by 

 having their Ijodies Ijuilt up of parts which are ari-anged in a more 

 or less star-like or " radiate " manner. Hence these creatures were 

 long known as " Radiate Animals." So many other animals of 

 dilt'erent kinds were, however, included in the old sub-kingdom 

 lladiata, that naturalists have generally abandoned this term. Most 

 of the Ccelenterate animals would come wider the popular term of 

 "Zoophytes" or jilant-animals (Gr. zoiin, animal; -phiiton, plant), 

 from the external resemblance which many of them bear to plants. 



Tbe i'fAnnterata may be defined as radiulbj sijmmetrk-al animals, 

 id irliirji tin; iiioulJi op/'iis into a simple or variously divided space, 

 'ir/iie/i rej:reseii/x t/o/ iihiiieittarii i:aritij of the higher animals. This 

 interned xpaee. mji;/ err may not he dirided into two portions — one 

 speeiidly et)nneeted yith digestion, and the other eorrespoiiding with 

 the body-cavity of the higher animals. The hody-iredl is composed 

 of tiro fundawentcd, layers {the " n-todirvi" n,.el '' eiidodenn"). The 

 nercpus system, is repre.vnted hy rlijfnseil ganglion-eelh, or sometimes 

 hy a simple nerre-ring ; hnt there are no •■innlatory organs. Distinct 

 reprodiwtire organs are pre.tent at some p, riod or another of life ; hut 

 nnn-se:aial reproduetion is eery general. 



Tlie leading feature which distinguishes the Colenterata, and the 

 oni' from which the name of the sub-kingdom is derived, is the 

 peculiar arrangement of the digestive system. In the Protozoa, as 



