PREFACE. XIU 



Zoophytes present to the physiologist, the simplest indepen- 

 dent structures compatihle with the existence of animal life, 

 enabling him to examine some of its phenomena in isolation, 

 and free from the obscurity which greater complexity of 

 anatomy entails : the means of their propagation and increase 

 are the first of a series of facts, on which a theory of genera- 

 tion must rise ; the existence of vibratile cilia on the surfaces 

 of membranes, which has since been shewn to be so general 

 and influential among animals, was first discovered in their 

 study ; and in them are first detected the traces of a circula- 

 tion carried on independently of a heart and vessels."^' The 

 close adhesion of life to a low organization ; its marvellous 

 capacity of redintegration ; the organic junction of hundreds 

 and thousands of individuals in one body, the possibility of 

 which fiction had scarcely ventured to paint in its vagaries, 

 have all in this class their most remarkable illustrations. 

 On the geologist zoophytology has peculiar claims. Its sub- 

 jects are, apparently, the first of animals which were called 

 into existence ; and from that high date to this time, they 

 have played a part in the earth''s mutations, from chaos to 

 the present well ordered scene, greater perhaps than any 

 other class of beings. Separating from the waters of the 

 ocean the calcareous matter held in solution, they reduce it to 

 a solid state ; constructing therewith their varied polypidoms 

 or corals which, by their continual growth, their coalescences, 

 their enormous numbers and extent, first roughen the smooth 

 basin of the sea, raise up reefs and ridges that obstruct the 

 hitherto open course of navigation, and become ultimately 

 the foundation of islets and islands that remain the " monu- 

 mental relics " of the puny race. As now the process and 

 change goes on in tropical seas, — so operated it, in the preada- 



* On the importance of the study of inferior organisms to the physiologist, see 

 Carpenter's General and Comparative Phj'siology, p. 4 ; and Owen's Lectures on 

 Invertebrate Animals, p. 5. (Note to 2nd edit.) 



