870 POLYPI. 



feet animal. Most of the same species, besides, form compound animals, 

 adhering to one another by lateral appendages, or by their posterior extremi- 

 ty, and participate in a common life without ceasing to enjoy their indivi- 

 dual and independent existence. The mode of reproduction in many 

 individuals of this class is unknown. In general, it may be remarked, that 

 many are conceived to be gemmiferous, or to extend the race by buds in the 

 manner of plants, while others propagate the species by means of ova. In 

 the lowest of the races, the distinctive characters of animal life are so faintly 

 drawn, that with difficulty can many of these be distinguished from the 

 Cryptogamic families of the Vegetable Kingdom. Many of the Polypi have 

 the faculty of forming fixed envelopes, more or less solid, in which they re- 

 side. The singular diversity of this envelope, in its own substance inor- 

 ganic and calcareous, and its accumulation in immense masses in the seas 

 of warm countries, by the combined operation of these animals, is not the 

 least interesting fact in their history. They appear in these countries to 

 multiply with such facility, and in such great abundance, as to become pow- 

 erful agents in the modification of the surface occupied by the ocean. Isl- 

 ands are reared, and coasts extended, by the incessant multiplication of 

 these animals. M. Lamarck conjectures that even the calcareous mountains 

 and strata of the present surface of the globe may have been formed in the re- 

 volution of ages by Polypi ; and that future changes in this surface, and in 

 the level of the ocean, are in course of preparation by these minute animals. 



The animals of this class were regarded by the older naturalists as stony 

 vegetables, or vegetating stones, and a number of theories were franfied to 

 explain their formation and growth. Their animal nature was first conjec- 

 tured by Imperati, in 1699, proved in 1727, by Paysonnel, and confirmed in 

 1740, by the observations of Trembley upon the Hydrae. From this period, 

 the true knowledge of these animals continued to increase, chiefly through 

 the researches of Ellis. Marsigli, Baster, Donati, Boccone, Degeer, Reau- 

 mur, Jussieu, and Cavolini, followed in the path traced out by Ellis and 

 Linnaeus, with the same success 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 orders — the first comprehending the naked Polypi ; and the 

 second those which live in polypiferous masses, formed by their united 

 labors. The second order is further subdivided into many families. La- 

 marck, whose system regarding these animals is followed in the present 

 work, divides the class of Polypi into five orders. 



I. Polypi Natantes. — Tentaculated polypi, united in a common fleshy 

 body on an axis, free, and floating in the water. 



