870 POLYPI. 
fect 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 indiv:- 
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 inbr- 
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 framed 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 Hydre. 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 
Linneus, 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 hassince been done by 
Pallas, Bruguieré, and Lamarck. Cuvier, in his Régne 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. Thesecond 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. Poryrr Narantes. —Tentaculated polypi, united in a common fleshy 
body on an axis, free, and floating in the water. 
