414 INVERTEBRATES 



ments answering the purpose of feet. These are little hollow 

 cylinders, composed of a membranous substance, and ending in a 

 kind of knob, which is also hollow. They are filled with a liquid, 

 which is furnished to them by reservoirs situated within the body. 

 The animal; at will, can either lengthen these cylinders and dis- 

 tend their extremities, by forcing this liquid into them, or exhaust 

 it, and thus shorten and contract them. When it is exhausted, 

 the i;nob or disk is drawn into a cuplike form, and thus may be 

 firmly fixed to whatever object it is applied, like a cupping-glass; 

 and when the liquid is again thrown into it, it is again loosened. 

 By this arrangement, which enables it to fix and loosen, and at 

 the same time to lengthen and shorten these organs of motion, 

 the animal is enabled to move itself from place to place. Some 

 of the animals of this order are composed of several branches 

 united together in one common centre, like the spokes of a wheel ; 

 and hence they are called star-fish, or more commonly five-fingers. 

 Their mouth is in the centre, where the several branches meet. 

 Others are globular, and others oblong, like the sea-urchin and 

 sea-egg. 



The Intestinal Worms belong also to the class of Zoo- 

 phytes. Those which inhabit the bowels of children are well 

 known. But there is scarce any animal which is not infested by 

 one or more kinds of them. They can exist only within the bodies 

 of the animals to which they beiung, and it is seldom that the same 

 species infests more than one kind of animal. They have no visi- 

 ble organs of respiration or circulation, and those of digestion are 

 viry imperfect and indistinct. They are not confined to the intes- 

 tines, but are found in other canals and passages of the body, and 

 even in the substance of parts, as in the liver, brain, and eye. 

 The difficulty of accounting for their existence in these parts, has 

 given rise to the opinion of some naturalists, that they are spon- 

 taneously engendered ; but it is known, with regard to many ol 

 them, that they produce eggs, and a living oflFspring; and it is con 

 trary to all the analogy of nature to ascribe, in these obscure cases. 

 to chance and the spontaneous operations of matter, the produc- 



