* 



XVi INTRODUCTION. 



scale of existence are the Polypi — creatures pos- 

 sessing the form of a vegetable, with the consist- 

 ence of a jelly. Their internal organization con- 

 sists only of a sac, the first indication of a sto- 

 mach. They have no head, nor organs of sense, 

 muscles, nor vessels. Like plants, they perpe- 

 tuate their species by buds. They live in water. 



The next class of animals, also aquatic, are of 

 a star-like form. Besides the mouth and stomach 

 common to them with the polypi, slight indications 

 of a nervous and respiratory system are discover- 

 able in their organization. None of their move- 

 ments seem connected with muscular action, though 

 their substance in many instances is capable of 

 contraction and dilatation. They are multiplied, 

 not only by buds or gemmae, but also by eggs, 

 where the new individual, separating from the pa- 

 rent, is thrown off by the mouth : they live in the 

 ocean. 



Worms have the organs of locomotion more 

 fully developed, the body of the animal being 

 divided into rings, — a faint approach to the ar- 

 ticulation of the limbs in more perfect creatures. 

 The long intestinal canal is widened at one part, so- 

 as to give a notion of the division into stomach and 

 intestine. They possess a circulatory system of 

 vein and artery, but no heart. Their respiratory 

 organs are of the simplest kind. They are fur- 

 nished with a long nervous cord, running from one 

 extremity of the body to the other, in the course 

 of which nodules of nervous matter are placed, 

 from which little nerves are radiated to the neigh- 



