1 2 8 PENNA TULIDJE. PART in. 



shaped stem and branches, covered by a scarlet coat, 

 having the polypes also only on the upper surface. 



The Pennatulidse, or sea-pens, which are the third 

 family of the Alcyon zoophytes, bear a great resemblance 

 to a goose's feather. The genus Pennatula has a flatly- 

 feathered, upright, calcareous axis, the bare part of 

 which is analogous to the quill ; but, instead of being 

 fixed like the stem of a Gorgon, it is merely stuck into 

 sand or mud at the bottom of the seas, while the upper 

 feathered part, containing the polypes, remains in the 

 water. The axis decreases in thickness upwards, and 

 the pinnules, which diverge from it transversely like 

 wings, are angular, thin, membranaceous, and strength- 

 ened by spicules. The whole animal is covered with a 

 soft fleshy tissue ; the polypes, which have eight pin- 

 nated tentacles, are arranged in a single row along the 

 edges of the pinnules, with their visceral extremities 

 prolonged into the soft tissue, so as to give it a tubular 

 structure, through which the nourishing juice prepared 

 by the polypes is carried for the maintenance of the 

 general envelope, the refuse being thrown out at their 

 mouths. When the sea-pens leave the mud or sand, 

 they do not swim actively with their pinnules, but move 

 languidly at the bottom. The Pennatulse are phospho- 

 rescent ; they are of a dull reddish brown during the 

 day, but at night they shine with the most brilliant 

 iridescence. In the tropical seas they occasionally 

 exceed a foot in length; in the cool latitudes they are 

 not more than five or six inches. The Pennatula phos- 

 phorea, found on the British coasts, has a hollow axis, 

 occupied by a well-developed stylet ; long pinnulse sym- 

 metrically disposed on each side of the middle and upper 

 part of the axis ; the polypes, which are very contrac- 

 tile, are arranged transversely on their upper and an- 

 terior edges ; the pinnae of the wings are scythe-shaped, 

 and furnished with a vast number of sharp spicules, 



