418 POLYPI. 



Many of the Polypi have the faculty of forming fixed enve- 

 lopes, more or less solid, in which they reside. The singular 

 diversity of this envelope, in its own substance inorganic and 

 calcareous, and its accumulation in immense masses in the seas 

 of warm countries, by the combined operations of these ani- 

 mals, is not the least interesting fact in their history. They 

 appear in those countries to multiply with such facility, and in 

 such great abundance, as to become powerful agents in the mo- 

 dification of the surface occupied by the ocean. Islands are 

 reared, and coasts extended, by the incessant multiplication of 

 these animals. M. Lamarck conjectures that even the calca- % 

 reous mountains and strata of the present surface of the globe 

 may have been formed in the revolution of ages by Poly- 

 pi ; and that future changes in this surface, and in the level 

 of the ocean, are in the course of preparation by these minute 

 animals. 



The animals of this class were regarded by the older natura- 

 lists as stony vegetables, or vegetating stones, and a number of 

 theories were framed to explain their formation and growth. 

 Their animal nature was first conjectured by Imperati in 1699, 

 proved in 1727 by Peysonnel, and confirmed in 1740 by the ob- 

 servations of Trembley upon the Hydros. From this period the 

 true knowledge of these animals continued to increase, chiefly 

 through the researches of Ellis. Marsigli, Baster, Donati, 

 Boccone, Degeer, Reaumur, Jussieu, and Cavolini, followed in 

 the path traced out by Ellis ; and Linnaeus, with the same suc- 

 cess which attended his investigations of the other objects of 

 nature, arranged the whole in his class Vermes, making them 

 an Order under the name of Lithophyta. The classification of 

 this great naturalist, who fixed the characters of the divisions, 

 and described the greatest number of species, forms the basis of 

 what has since been done by Pallas, Bruguiere, and Lamarck. 

 Cuvier, in his Regne Animal, divides the Polypi into two or- 

 ders, the first comprehending the naked Polypi; and the se- 

 cond those which live in polypiferous masses formed by their 

 united labours. The second order is further subdivided into 

 many families. Lamarck, whose system regarding these ani- 

 mals is followed in the present work, divides the class of Poly- 

 pi into five orders. 



