Order 3. COEALLIFEEI. 677 



Natantes, — 

 "Which form the third tribe of the coral family, liave the axis stony, but not fixed. They consist of 

 two principal genera, but each admits of subdivision. 



Pennatula. 

 This genus liave a common body, perfectly free, and susceptible of locomotion by the contractions of 

 its fleshy part, and the joint action of all the polypi. The contractions and dilatations are produced 

 by fibrous layers, which are embedded in the fleshy substance. The axis is a single stony column, and 

 the polypi generally have eight toothed tentacula. Whatever may be their form, one extremity is 

 always without polypi, and resembles the barrel of a feather — hence the name. Most of them can 

 emit a bright phosphorescent light ; and though their general habit be to swim freely in the water, some 

 species fix themselves in the sand, or get entangled in the folds of submarine bodies ; but they never 

 form an adhesion. 



Pennaiula, properly so called, have the portion without polypi cylindrical and with a blunt point ; and the other 

 part furnished on both sides with lamina; of various length and breadth, which are supported by tough bristles ; 

 but these bristles are not articulated upon the stony axis. The polypi are situated between these laminse. Several 

 species are found in the Atlantic and Mediterranean. Virgularia, have the laniinie much shorter. Scirpearia, 

 have the body slender, and the polypi detached and alternate. Pavonaria, are also slender, but the polypi are 

 arranged in quincunx on one side only. Renilla, have the body short with filaments, and a kidney-shaped disc on 

 one side, bearing the polypi. VereliUtim, are cylindrical, but without any branches; and the axis is usually small 

 and the polypi large. Ombellularia, have a very long stem with a tuft of polypi at the end. 



There are many small and porous stony bodies found in a fossil state, and in the sea, which, if they 



were invested with a living integument and polypi, would rank very nearly with this tribe. They are 



Ovolites, Lunulites, Orbulites, and others. 



Alcyonium, 



■Which, with Spongia, forms the fourth tribe, has the polypi with eight arms, and the intestines in a 

 common mass with the ovaries. It is not, however, supfovced by a stony axis; but always fixed to 

 the body ; and when it is drawn out into trunks and branches, these present nothing internally but 

 gelatinous matter. The covering is hard, and marked with furrows, into which the polypi retire. 



A. digitatum, the Sea Hand, divided into short and thick branches, and A. exos, with the branches smaller, and 

 of a fine red, are the most common in the European seas. Linnaeus and his followers included with this genus 

 the Theihtia, which have the interior roughened by long spiral lines of silicious matter, which unite in an equally 

 silicious nucleus. The crust, like that of the Sponges, presents two kinds of openings, one for admitting water, and 

 another for ejecting it. 



Spongia (Sponges), — 



Are well known as fibrous marine bodies, whose only sentient portion appears to be a sort of thin gela- 

 tine, which soon dries off. No polypi have been observed in them ; and our knowledge of their real 

 nature is very obscure. All the analogies, however, point them out as being animal, and not vegetable, 

 The forms which they assume are almost iuuumerable. 



THE FIFTH CLASS OF THE RADIATA. 

 THE INFUSORIA. 



It is usual to place at the close of the Animal Kingdom, these beings, which are so small 

 as to be in general inscrutable by the naked eye ; and which have been known only since 

 the microscope brought, as it were, a new world within the scope of our observation.' 

 [Every increase of extent of magnifying power and clearness of view, which the suc- 

 cessive improvements of the microscope have enabled us to obtain, has been rewarded 

 by new discoveries in the numbers, the forms, and the organization of these minute 

 animals. Farther improvements in the structure of the instrument, and the mode of 

 using it, may enable the observers of a future age to obtain information relative to this 

 part of the Animal Kingdom, of which we of the present age can form no adequate 



