16 MECHANICAL FUNCTIONS. 



injury. In like manner the Gordius, a worm resembling 

 a horse-hair, which inhabits stagnant pools, may be 

 dried, when it has no more signs of life than a piece of 

 wire, and again revived to life by immersion in water. 

 This animal is supposed by many to have derived its 

 existence from a horse-hair accidentally falling into the 

 water. But it is hardly necessary to say that such mis- 

 takes call for a more general knowledge of Animal 

 Physiology. 



We shall begin our physiological descriptions with 

 the most simple organizations, and gradually passing 

 through those which are more and more complex, finally 

 come to that of our own species. 



SPONGE. 



The remains of this animal are in such universal use, 

 and consequently so well known as to require no gene- 

 ral description. It belongs to an order of animals called 

 Zoophytes, which also includes the Corals, the Polypi, 

 and several other races which are only a single grade 

 above vegetables. This order indeed appears to be the 

 connecting link, between the animal and vegetable 

 kingdoms. The term Zoophytes signifies " animated 

 plants." 



The Sponges, of which there are manv species, are 

 all marine animals, living at the bottom of the sea, where 

 they are firmly attached to rocks and stones. 



These productions in general appearance much more 

 nearly resemble plants than animals ; but in their inter- 

 nal organization and structure they differ entirely from 

 vegetables. Their animal nature is clearly shown by 

 chemical analysis, and by the voluntary motion of some 

 of their parts which resembles respiration. 



Every part of the surface of a living Sponge presents 

 to the eye two kinds of orifices ; the larger having a 

 rounded shape, and generally a little raised on the mar- 



What is said of the gordius'? To what order of animals does the 

 sponge belong 1 What is the meaning of the term zoophytes 1 How is 

 the animal nature of the sponge indicated 7 What is said concerning 

 the orifices of the living sponge 1 



