SEA-MATS AND SHELLY CORALLINES. 67 



tacles. The contraction of these bands draws in the 

 integument, like the drawing of a stocking within itself, 

 and forces down the viscera into the cavity of the cell, 

 which is probably filled with the vital juices. 



Besides the hind bands, there is one, or a pair of 

 similar muscular bands attached on each side of the front 

 part of the base of the cell, and inserted similarly into the 

 neck. By watching the contraction of these, you will be 

 enabled to determine the use of the membrane-covered 

 aperture up the front of the cell At the moment of the 

 retraction of the viscera into the cell, a large angular 

 membrane is forced outward from the front side, which is 

 protruded more or less in proportion to the degree of 

 withdrawal of the polypide ; and as the latter emerges 

 again, the membrane falls back to its place. It is evident, 

 then, that this is a provision for enlarging the cavity ; the 

 walls are horny, and probably almost inelastic ; but when 

 the stomach forces the intestine forward, and the thick 

 gullet is bent outward by the withdrawal of the neck and 

 tentacles, the needful room is provided by the bulging out 

 of this elastic membrane, which recovers its place by the 

 pressure of the surrounding water, when the pressure of 

 the fluids within is removed. 



Now, after watching these movements of the polypides, 

 and the various structures whose forms and limits those 

 movements reveal, it will become manifest to you that 

 there is no visible organic connexion between the animal 

 distinctively so called and the curious bird's head. Thig 

 latter has a muscular system of its own, by means of 

 which its energetic motions are performed ; but it appears 

 quite isolated on the outside of the calcareous cell, and 

 wholly cut off from the interior by the knob on which it , 

 works, and by the thickness of the cell wall. Both knob 

 and wall appear quite imperforate ; and yet we cannot but 

 presume that some connexion exists, perhaps through the 

 medium of an exceedingly delicate and subtile, but living 

 F 2 



