ITS DOOR AND HINGE. 143 



extremity of Tvliich was surrounded by an extremely 

 delicate fringe or frill of filmy rays united by a den- 

 tated or vandyked membrane, closely resembling that 

 of Eucratea. Tlie appearance of the protruded mem- 

 brane and the cell, I have very carefully copied at 

 Fig. 9 ; but the relation of the parts to each other is 

 very difficult to understand. The interior of the 

 sheath contains many very slender threads constantly 

 waving with a vermicular motion; indeed they might 

 be mistaken for minute intestinal worms. They are 

 probably long ciliary hairs. 



Aug. \^th. A stem of Plunmlaria cristata, itself 

 parasitic on the shell of a Crab, was covered for 

 its basal half with a numerous colony of Anguinaria 

 scutulata, and for its terminal half wdth one equally 

 crowded of Plum, setacea. An examination of the 

 former enables me to add a little to my knowledge of 

 this curious zoophyte. I perceive that the terminal 

 extremitv of the head is furnished with a sort of door 

 that works on hinges. When the polype is throughly 

 retracted, this is closed, and held firmly down by 

 means of a ligamentous muscle fastened to its interior, 

 and connected with the animal. When the latter 

 relaxes, the door begins to open, I presume by the 

 elasticity of the hinge acting as a spring; and as the 

 polype protrudes, the door in proportion falls back, 

 until it makes more than a right angle with its closed 

 position. It appears to consist of a half- ring of homy 

 substance, across which is stretched a delicate mem- 

 brane, continuous with that which covers the large 

 ventral aperture. I have seen it in many individuals, 

 in various aspects and positions, and have witnessed 



