I40 



CCELENTERATA OR STINGING- ANIMALS. 



which extend in a vertical ridge along them, are turned away from 

 one another and run on the inter-septal surfaces, whereas in the other 

 mesenteries the retractor muscles run on the intra-septal surface, those 

 of a pair facing one another. The arrangement of these muscles is 

 of great importance in classifying Anthozoa. It is probable that the 

 mesenteries are homologous with the tseniolse of jellyfish, and the mes- 

 enteric with the gastric filaments. 



Development. — Comparatively little is known in regard to the early 

 stages of development in sea-anemones. From the fertilised ovum, a 

 blastosphere may result which by invagination becomes a gastrula. _ Or 

 the two layers may be established by a process known as delamination, 

 in which the cells are divided into an inner endodermic and an outer 

 ectodermic layer. 



Related Forms. — The Sea- Anemones are classified in the sub-class 

 Anthozoa or Actinozoa, and along with many corals are distinguished 

 as Zoantharia or Hexacoralla from the Alcyonaria or Octocoralla, like 

 Alcyonium and related corals. This contrast is not perfectly satisfac- 

 tory, but it rests on such distinctions as the following : — 



Anthozoa or Actinozoa. 



Zoantharia, Hexacoralla, c.g.^ 

 Sea-Anemone. 



Many are simple, many colonial. 



Tentacles usually simple, usually some 

 multiple of six, often dissimilar. 



Mesenteries usually some multiple of six, 

 complete and incomplete. 



Retractor muscles never as in Alcyonaria. 



Two gullet grooves or siphonoglyplies, or 



only one. 

 Dimorphism only in some Antipatharia, 



and in one Madrepore coral. 

 Calcareous skeleton if present is derived 



from the basal ectoderm. 

 Types. 

 Actiniaria. Sea-Anemones. 



Madreporaria. Reef-building corals. 

 Antipatharia. Black corals. 



Alcyonaria, Octocoralla, e.g.^ 

 Deau-Men's-Fingers. 



All colonial, except a small family includ- 



ing Monoxenia and Hazjnea. 

 Tentacles eight, feathered, uniform. 



Mesenteries eight, complete. 



Retractor muscle always on one (ventral) 

 side of each mesentery. 



One (ventral) gullet-groove or siphono- 

 glyphe, or none. 



Occasional dimorphism among members 

 of a colony. 



There are usually calcareous spicules (of 

 ectodermic origin) in the mesoglcea. 

 Exmnpies. 



A Icyonium (Dead-men's-fingers), with 

 diflFuse spicules of lime. 



Tuhipora (Organ - pipe coral), with 

 spicules fused into tubes and trans- 

 verse platforms. 



Corallinm rubrtun (Red-coral), with an 

 axis of fused spicules. 



Isis^ with an axis of alternately limy and 

 horny joints. 



Pennaiuia (Sea-pen), a free phosphor- 

 escent colony, with a '* horny" axis 

 possibly endodermic. 



Heliopora^ blue coral. 



Coral-Making.— 1<!^ have already noticed that there are "corals" 

 among the Hydrozoa, viz., the Millepores. Leaving these out of ac- 

 count, we have to recognise that both divisions of Anthozoa include 

 many corals. 



