POLYPS. 63 



their mouth admits of much expansion : and the body can be dis- 

 tended. The food is moved to and fro in the cavity of the body, 

 and in a short time (often within a quarter of an hour) is .converted 

 into a pap. The undigested residue is rejected through the mouth. 

 Propagation is effected usually by buds. A minute swelling rises 

 on the surface of the Polyp; it grows, loses its conical form, be- 

 comes tubular, acquires tentacles, and is then a new Polyp. The 

 young animal continues to sit on the body of the parent, and thus 

 receives the same nutrition in common. Upon this young one 

 other young buds may be developed. Thus a branching arises. 

 At length the young Polyp separates itself from the parent stem 

 (in summer frequently after four days, in winter later), assumes an 

 independent state, and new buds are formed, or those already 

 present are multiplied. 



Thus these Polyps may form compound animals. Many indi- 

 viduals of the same species are united so as to make up a single 

 body. All the animals thus combined gain their nutrition in com- 

 mon, have a common life. It is not the animal kingdom only 

 that affords us instances of compound living bodies : the vegetable 

 kingdom presents many such 1 . By an individual, in the vegetable 

 and animal kingdoms, may be understood a body that cannot be 

 divided into two or more similar portions, without the idea of a whole 

 being lost, and whose vital functions pass through a determinate 

 cycle of periods 2 . The development of the fruit is the final function 

 in vegetable life: when this is accomplished the plant may die. 

 Many plants bear fruit only once whether in one year, or in two 

 or more years ; such plants die after fructifying, and are true indi- 

 viduals. There are other plants again, which leave a determinate 

 portion after the fructification, that continues to live, and, after a 

 time, bears fruit anew. The portion that thus remains may con- 

 sist of root alone, or of root and stem. Such plants are, in reality, 

 compound. 



A tree therefore is not an individual, not a single plant. The 

 buds of the tree are new plants : they are developed, grow, possess 

 an independent life, which is 'passed in determinate stages. Hence 



1 See LAMARCK, Hist. Nat. des anint. sans vert. I. p. 69, &c. (and 2nd edit. p. 65, 

 &c.). Comparaison des Animaux composts avec des vegetaux pareillement composes. 

 3 See SCHLEIDKN in MUELLER'S Arckiv. 1838. a. 168. 



