ON POLYPS. 



developes within its substance the skeleton peculiar to its species, 

 exhibiting by degrees the form of the individual from which it 

 sprung. It is curious to observe the remarkable exception which 

 sponges exhibit to the usual phenomena witnessed in the reproduc- 

 tion of animals, the object of which is evident, as the result is 

 admirable. The parent sponge, deprived of all power of movement, 

 would obviously be incapable of dispersing to a distance the numerous 

 progeny which it furnishes ; they must inevitably have accumulated 

 in the immediate vicinity of their place of birth, without the possi- 

 bility of their distribution to other localities. The seeds of vegetables, 

 sometimes winged and plumed for the purpose, are blown about 

 by the winds, or transported by various agencies to distant places ; 

 but, in the present instance, the still waters in which sponges grow 

 would not have served to transport their progeny elsewhere, and 

 germs so soft and delicate could hardly be removed by other 

 creatures. Instead therefore of being helpless at their birth, the 

 young sponges can, by means of their cilia, row themselves about 

 at pleasure, and enjoy for a period powers of locomotion denied to 

 their adult state. 



CHAPTER III. 



ON POLYPS. 



Zoophytes of old Authors Phytozoa (Ehrenberg). 



(20.) IT is not surprising that many members of the extensive 

 family upon a consideration of which we are now entering, should 

 have been regarded by the earlier naturalists as belonging to the 

 vegetable kingdom, with which, in outward appearance at least, 

 numerous species have many characters in common.* 



Fixed in large arborescent masses to the rocks of tropical seas, 

 or in our own climate attached to shells or other submarine sub- 

 stances, they throw out their ramifications in a thousand beautiful 

 and plant-like forms ; or, incrusting the rocks at the bottom of the 

 ocean with calcareous earth separated from the water which bathes 

 them, they silently build up reefs and shoals, justly dreaded by 

 the navigator, and sometimes giving origin, as they rise to the 

 surface of the sea, to islands which the lapse of ages clothes with 



* Tournefoit, Institutiones Rei Herbaria*, 4to. 1719. 



