1 62 



THE INVERTEBRATA 



endodermal. The secondary polyps are budded off from endodermal 

 tubes which ramify in the much thickened mesogloea of the body wall 

 of the primary polyp, and belong to two types of individuals, the normal 

 autozooids which feed the colony and the siphonozooids , with reduced 

 mesenteries and enlarged siphonoglyph, whose only function is to 

 maintain the circulation of water in the canals of the colony. The 

 autozooids in Pennatula are arranged in rows side by side to form 

 equal and regular lateral branches on each side of the axis giving the 

 colony its feather-like form, and the siphonozooids are mainly found 



Fig. 134. Gorgonians (two species on the left) and hydrocorallines (on the 

 right) growing on a coral reef in Florida. From an underwater photograph 

 by Professor W. H. Longley. 



on the back of the axis. A colony has a limited but remarkable power 

 of movement and can burrow into sand or mud by its basal stalk. 



In two genera, Tuhipora (the organ-pipe coral) and Heliopora 

 (the blue coral), which are widely distributed on coral reefs, a con- 

 tinuous calcareous skeleton is developed resembling that of reef corals. 

 The polyps of Tuhipora are elongated and parallel and connected by 

 stony platforms which are traversed by the endodermal tubes. But 

 while in Tuhipora there is an internal skeleton developed as in 



