SPONGES. 155 



as completely stationary as that of plants, yet 

 such is not the condition of the earlier, and more 

 transitory stages of their developement. Nature, 

 ever solicitous to provide for the multiplication 

 of each race of beings, and for their dissemina- 

 tion over the habitable globe, has always pro- 

 vided effectual means for the accomplishment of 

 these important ends. The seeds of plants are 

 either scattered in the immediate neighbourhood 

 of the parent, and take root in the adjacent soil, 

 or are carried to more distant situations by the 

 wind or other agents. In the animal kingdom, 

 the young offspring of those races which are en- 

 dowed with a wide range of activity, are reared 

 on the spot where they were produced, either by 

 the fostering care of the parent, or by means of 

 the nourishment with which they are surrounded 

 in the egg, and there remain until the period 

 when, by the acquisition or extension of locomo- 

 tive powers, they are enabled, in their turn, to 

 go in quest of food. But in the tribes of ani- 

 mals at present under our consideration, this 

 order is reversed. It is the parent that is 

 chained to the same spot from an early period 

 of its growth, and it is on the young that the 

 active powers of locomotion have been conferred, 

 apparently for the sole purpose of seeking for 

 itself a proper habitation at some distance from 

 the place of its birth; and when once it has 



