82 



INVEIiTEBKATE ANIMALS. 



tlie latter organs, but are destitute of a mouth. The body-cavities 

 of all the zoijids are placed in commuuicatiou by means of canals 

 which ramify in tlie .'ijioiig}' skeleton. 



;. 4i>. — Enlarged view of a portion of tlie surface of a livirirr colony of MiUepora 

 (Nii/'-sa, showing the expan'tfl znoirls of a .single system, a. Central " gastrozooid " ; 

 b, (Jne of tlic nioutbless " diietylozooii-ls." (After Jloseley.) 



Other living Hydrocorallines are the coral-like Sti/Iaster, AUopora, 

 &c. Closely allied to the recent types above menti<jned is a great 

 series of fossil and wholly extinct organisms, of which Stromatopora 

 may be regarded as tlie central form. 



