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(free below the gullet), and the mesenterial filaments or 

 folds of the free edges of the mesenteries. 



Explain the Structures seen in a transverse Section of the 

 Polyp of Alcyonium (a) through the Stomodceum 

 Region, (b) below the Stomodceum. 



(a) The wall of the polyp tube consists of outer ectoderm 

 and inner endoderm with a thickened mesoglcea between. 



Outgrowths of the wall, the eight mesenteries, pass 

 across to the central gullet or stomodseum, and thus the 

 ccelenteron cavity is partitioned into eight chambers. 



The gullet has (at the so-called ventral side) a deep 

 ciliated groove called the siphonoglyph. 



On the ventral sides of the eight mesenteries (i.e., the 

 sides facing towards the siphonoglyph) there are powerful 

 longitudinal muscles. The two mesenteries at the siphono- 

 glyph side are the directive mesenteries. 



. (&) The mesenteries are free, and upon their free edges 

 are the mesenterial filaments. Otherwise the structure is 

 similar in both sections. 



What is the Function of (a) the Siphonoglyph, (b) the longi- 

 tudinal Muscles ? 



The siphonoglyph, by means of its powerful cilia, keeps 

 up the water current when the outer part of the gullet 

 is choked with food and thus ensures respiration. 



By means of the longitudinal or retractor muscles the 

 polyp can suddenly draw in. 



Order Zoantharia. 



Comparing a Sea-anemone (e.g., Actinia or Peachia) with 

 Alcyonium, what are the chief Structural Differences ? 



Ordinary sea-anemones do not form colonies, Their 

 hollow tentacles are not pinnate and are numerous (Peachia 

 has twelve). There are six or more pairs of primary mesen- 



