168 FUNCTIONS AND INSTINCTS. 



sidered as nearer to vegetable matter than the 

 other polypes. 



5. Other Alcyons 1 seem to have a more com- 

 plex organization than any of the preceding 

 polypes ; they are stated to have eight parallel 

 stomachs. Only four genera belonging to this 

 Order have been described, and its proper station 

 seems doubtful. 



6. In the Sea-Pen, and others, 2 the animal 

 envelopes an axis, as in the third Order, and 

 has a tentacular mouth, but it is not fixed by its 

 base. The greater part of these animals float in 

 the waters, but others remain at the bottom, 

 either upon the surface or partly plunged in the 

 sand. 



Polypes are invariably aquatic animals, some 

 inhabiting fresh water, but the great body are 

 marine, and most numerous in tropical seas. In 

 very high latitudes, only cellarians, 3 sertularians, 4 

 alcyons, and some sponges occur, and in the 

 vicinity of volcanic islands in the Polar seas, 

 corallines and gorgonians. These multiply a 

 little from 6 to 9 N. L. : then, as they ap- 

 proach the tropics, the coral reddens, and the 

 madrepores whiten, and at 33 they attain their 

 full powers of growth and multiplication. Some 

 frequent the mouths of rivers, where there is a 

 conflux of fresh and salt water. Some love 



1 Polypi tubiferi, Lam. 2 Polypi natantes, Lam. 



3 Cellaria. 4 Sertularia. 



