166 REPRODUCTION. 



slightest resemblance to the adult polyp. As in the young 

 Medusa, the body is cylindrical, covered with 

 delicate cilia. After having remained free for 

 some time, the young animal fixes itself and as- 

 sumes a flattened form. By degrees, a little swell- 

 ing rises from the centre, which elongates, and at 

 last forms a stalk. This stalk ramifies, and we 

 soon recognize in it the animal of figure 143, 

 with the three kinds of buds, which we may 

 consider as three distinct forms of the same animal. 



350. The development of Campanularia presents, in 

 some respects, an analogy to what takes place in the re- 

 production of plants, and especially of trees. They should 

 be considered as groups of individuals, and not as single 

 individuals. The seed, which corresponds to the embryo 

 of the Hydroid, puts forth a little stalk. This stalk soon 

 ramifies by gemmiparous reproduction, that is, by throwing 

 out buds which become branches. But ovulation, or repro- 

 duction by means of seeds, does not take place until an ad- 

 vanced period, and requires that the tree should have attained 

 a considerable growth. It then produces flowers with pistils 

 and stamens, that is, males and females, which are com- 

 monly united in one flower, but which in some instances are 

 separated, as in the hickories, the elders, the willows, &c.* 



* Several plants are endowed with organs similar to the third form of 

 buds, as seen in the Campanularia ; for example, the liverwort, (Marchan- 

 tia polymorpha,) which has at the base of the cup a little receptacle, from 

 the bottom of which little disk-like bodies are constantly forming, which, 

 when detached, send out roots, and gradually become complete individu- 

 als. Besides that, we find in these animals, as in plants, the important 

 peculiarity, that all the individuals are united in a common trunk, which 

 is attached to the soil ; and that all are intimately dependent on each 

 other, as long as they remain united. And if we compare, in this point 

 of view, the various species in which alternate reproduction has been 

 observed, we find that the progress displayed in each type consists pre- 

 cisely in the increasing freedom of the individual in its various forms. At 



