SPONGES. 141 



the condition of the earlier, and more transitory 

 stages of their developement. Nature, ever soli- 

 citous to provide for the multiplication of each race 

 of beings, and for their dissemination over the habi- 

 table globe, has always provided 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 endowed 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 and extension 

 of locomotive powers, they are enabled, in their 

 turn, to go in quest of food. But in the tribes of 

 animals 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 active powers of loco- 

 motion 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 made this selection, it there fixes 

 itself unalterably for the remaining term of its 

 existence.* 



* Phenomena still more curious are presented by a tribe of natural 

 productions, resembling aquatic plants in all their external cha- 

 racters, but, after a certain period, giving birth to an immense 

 number of animated globules, which, for a time, move briskly in the 

 fluid, like infusory animalcules, and then congregate together, and 



