CHAP. IV. MOTIONS OF ANIttALS. 93 



(112.) The locomotive powers of zoophytes are, in 

 general, exceedingly limited. Very many of them are 

 firmly fixed to stones, or rocks, from which they never 

 move; and their movements are, consequently, restricted 

 to those tentacula, or feelers, with which they seize upon 

 passing objects for food. Many polypes do this in a 

 rapid and violent manner ; but the process of swallowing 

 or absorbing this nourishment is carried on in a much 

 slower way ; while the amazing contractile and extensile 

 power which they possess, enables them to devour ani- 

 mals much larger than themselves." The Actinia, or 

 sea anemones, are said to have a very slow r progressive 

 motion, which is supposed to be performed by the base 

 being loosened from the place to which it was fixed, 

 the tentacula being employed as so many legs. These 

 tentacula are, indeed, peculiarly important auxiliaries to 

 this tribe; and Mr. Hughes, while observing one of 

 these singular creatures in the island of Barbadoes, no- 

 ticed four dark-coloured threads, somewhat resembling 

 the legs of a spider, which rose from the centre of the 

 animal, with a quick spontaneous motion from one side 

 to the other, and which he conceived to be arms, or 

 feelers which closed like forceps to secure and Detain the 

 prey. * In several sponges, a considerable motion has 

 been observed ; and Mr. Ellis assures us that one of the 

 cock's-comb sponges (Spongia cristata), which was 

 taken off the rocks near Hastings, in Sussex, on being 

 put into a glass vessel of sea water, could be perceived 

 to suck in and squeeze out the water " through the rows 

 of holes or little pores along the tops, giving evident 

 signs of life."t 



(113.) The most perfect or typical of bivalve shells 

 are free, and are thus endowed with locomotion ; but 

 several families are firmly fixed to other substances. 

 Among these latter are the edible oyster, and other spe- 

 cies of the same group. The abbe Dicquemaire, 

 however, informs us that the common oyster occa- 

 sionally moves itself by resorting to the singular ex- 



* Ellis's Hist, of Zool. p. 8 f U>id. p. 186. 



