THE CELL-MEMBRANE. 201 



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and the rectum, and the insertion of both into the 

 stomach. This retractation is in part eiFected by 

 a pair of longitudinal muscular bands, which are 

 inserted at the back of the bottom part of the cell, and 

 into the skin of the neck below the tentacles. 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- 

 (See Fig. 4). 



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 simi- 

 larly into the neck. It was while watching the con- 

 traction of these that I discovered with pleasure the 

 use of the membrane-covered aperture up the front of 

 the cell. At the moment of the retractation of the 

 viscera into the cell, a large angular membrane was 

 forced outward from the front side, which was pro- 

 truded more or less in proportion to the degree of 

 withdrawal of the polype, and as the latter emerged 

 again, the membrane fell back to its place. It is 

 evident then that this 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 

 withdi'awal 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. 



