30 BRITISH HYDROID ZOOPHYTES. 



of non-spilling inkstand). The preparation of 

 food is carried on by this portion. The 

 interior is called the body cavity, as distinct 

 from the stomach. 



Arising out of the body wall and directed 

 towards the pendant stomach or centre of the 

 animal, are certain little vertical fleshy plates 

 (Mesenteries). The anemones do not possess 

 these modifications, but the coral polyps do, 

 and in addition secrete carbonate of lime, or 

 horny coral, in the deposition of which the 

 mesenteries take part, by secreting what are 

 known as the " septa," or rays of the coral. 



Hydroids and Polyzoa compared. 

 There is so much outward similarity between 

 these hydroid-zoophytes and certain other 

 creatures of much higher standing, viz., the 

 Polyzoa and Bryozoa (Molluscoida) that it 

 may be desirable to point out the wide gap 

 which separates these two groups. 



In appearance, they have much in com- 

 mon. They are very minute ; they have the 

 habit of permanent budding (thereby produc- 

 ing plant-like growths) ; they secrete a poly- 

 pary-like covering ; the animals themselves 

 are transparent, and have a circle of tentacles 



