The Oral Arms and their Branch es. 

 I The eight oral arms (Fig. 26) arise from the central oral 

 disk at about equal intervals and, when an arm is extended, the 

 distance from the centre of the oral disk to the tip of the 

 arm about equals the diameter of the umbrella. But the anns 

 are very contractile and may be shortened to half this length. 

 The arms are slender and graceful in shape, the jelly tapering 

 very gradually to the tips of the finest branches. The bran- 

 ches are ai'ranged alternately. The largest one, which is the 

 one first formed, is at a point about two-thirds the length of 

 the arm from its base. From this point the branches gradually 

 decrease towards the base of the arm, and rapidly decrease to- 

 Iwi.rds its apex. The general outline of the ar-m, therefore, 

 including its branches, is roughly spatulate. 



The Oral Funnels and Brachial Appenda^;es . 

 Just below the surface of the oral side of each arm, there 

 is a longitudinal tube, the brachial canal , that ramifies to 

 each branch and finally opens to the exterior by funnel-shaped 

 oscula (os. Fig. 26) at the tips of the numerous ultimate 

 branches, and at many places along the course of the tube. 

 The margins of these oscula, or oral funnels are provided with 

 short, tentacle-like projections, or digitella. These are i 

 covered by an epithelium containing nettle cells and each has 



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