32 INTRODUCTION. 



from the circulation in closed vessels to nutrition by imbibi- 

 tioHj and the corresponding one of respiration in circumscribed 

 organs^ to that effected by tracheae or air-vessels distributed 

 throughout the body. In them, the organs of taste and sight 

 are the most distinct; one single family alone presenting that 

 of hearing. Their jaws, when they have any, are always 

 lateral. 



The fourth form, which embraces all those animals known 

 by the name of zoophytes, may also properly be denominated 



Animalia Radiatay 



Or radiated animals. We have seen that the organs of 

 sense and motion in all the preceding ones are symmetrically 

 arranged on the two sides of an axis. There is a posterior 

 and anterior dissimilar face. In this last division, they are 

 disposed like rays round a centre ; and this is the case even 

 when they consist of but two series, for then the two faces 

 are similar. They approximate to the homogeneity of plants, 

 having no very distinct nervous system or particular organs of 

 sense ; in some of them, it is even difficult to discover a ves- 

 tige of circulation j their respiratory organs are almost univer- 

 sally seated on the surface of the body, the intestine in the 

 greater number is a mere sac without issue, and the lowest of 

 the series are nothing but a sort of homogeneous pulp, endow- 

 ed with motion and sensibility.(l) 



(1) Before my time, modern naturalists divided all invertebrated animals Into 

 two classes. Insects and Worms. I was the first who attacked this method ; and 

 in a memoir read before the Society of Natural History of Paris on the 10th of 

 May 1795, and printed in the Decade Thilosophique, I presented a new division, 

 in which I marked the characters and limits of the Mollusca, Crustacea, Insects 

 and Worms, Echinodermata and Zoophytes. In a memoir read before the Insti- 

 tute on the 31st of December 1801, 1 ascertained the red-blooded worms or Anne- 

 lides. And finally, in a memoir read before the Institute in July 1812, and printed 

 in the Annales du Museum d'Histoire Naturelle, tome xix, I distributed these 

 various classes in three divisions, each of which is analogous to a branch of the 

 vertebrata. 



