238 Proceedings of the 



III. On the Prehensile Apparatus of Spio setieornis. By Thomas 

 Strethill Wright, M.D., &c. 



Description of Plate XII. 



Fig. 18. Section of tip of tentacle of Spio setieornis — a, wall of tentacle — b, 

 vessel — c, spine-bearing papillae. 



19. Enlarged sketch of one of the papillae. 



20. Tricho-eysts — a, entire — h, ruptured, and discharging spicules. 



1. Old shells taken from the sea are frequently found stud- 

 ded with small tubes, composed of mud and sand, cemented 

 together by slime. These tubes are the habitation of the An- 

 nelid Spio setieornis. When they are placed in water, we 

 presently see a pair of long glassy tentacles protruded from 

 each opening, which are tossed about with such an incessant 

 and violent motion that we are tempted to believe their con- 

 cealed owners have taken leave of their senses. If a small 

 piece of oyster is thrown amongst them, it is instantly seized 

 by the waving arms around, and pulled hither and thither, 

 until it is torn to pieces and devoured by the black-eyed and 

 wicked-looking little Annelids, which, forgetting their usual 

 coyness, protrude their heads from the tubes. We observe 

 that the tentacles, when seizing the oyster, attach themselves 

 to it not by winding themselves round it, but by simple adhe- 

 sion, as if they were studded with numerous suckers and 

 hooks, like the arms of the cuttle-fish. Anxious to examine 

 their microscopic structure, we make many attempts, by rapid 

 clips of our spring scissors, to possess ourselves of a pair of the 

 delicate white arms, but in vain. The Spio, who has all her 

 senses about her, twitches them in, and darts back deep into 

 the substance of the shell, from the mouth of which her tube 

 projects only a little distance. At last we make a successful 

 snip, and a tentacle is placed on the stage of the microscope, 

 still continuing its writhing motions, and gliding through the 

 water as though possessed of independent life. 



The tentacle of Spio, the tip of which is shown in fig. 18, 

 is a hollow tube of dense granular parenchyma, covered by a 

 thin layer of transparent tissue. Its interior is occupied by 

 a sinuous vessel, which, in the living animal, is constantly 



