42 ON THE PLACE OF MAN IN THE SCALE OF BEING. 



and the muscles, which are numerous and complex, are attached to the inte- 

 rior of these. In the Mollusca, the whole body is quite soft; and many spe- 

 cies exist, in which it has no external protection; in a large proportion of the 

 group, however, the surface has the power of producing shelly matter, so as 

 to form a protective habitation, within which the animal can withdraw its 

 body, but which does not exhibit any very definite type of form. In the 

 Radiata, all the parts are arranged in a circular manner, the mouth being in 

 the centre; some of them are protected by firmly-jointed external skeletons, 

 like those of the Articulata ; whilst others deposit calcareous matter in the cen- 

 tre of their soft fleshy structures, as if sketching out the internal skeleton of 

 the Vertebrata. The skeletons of most of the Inverteb.rata differ, however, 

 from those of Vertebrate animals, in this important character, that they are 

 not permeated by vessels, and are formed only by superficial deposition. 

 Hence they are termed extra-vascular : and it is an obvious result of an ar- 

 rangement of this kind, that parts once formed are never changed, except by 

 the ordinary processes of decay, and that they can only be extended by addi- 

 tion to their exterior ; whilst in Vertebrata, the bones are subject to alterations 

 of any kind, whether of removal or addition, throughout their entire substance. 

 It is not correct to regard them, however, as mere exudations, or as being des- 

 titute of vitality ; since they consist, in all instances, of a regularly-organized 

 tissue, in which the mineral matter, where such exists, is deposited ; and in 

 several cases they are traversed by tubes, which seem to convey a fluid de- 

 stined for their nutrition, if not actual blood. Fabrics of this kind are on the 

 same footing with the dentine and enamel of the teeth of Vertebrata ( 209, 

 210); to which they sometimes bear a very strong resemblance. A more 

 detailed account of the general structure of these sub-kingdoms will now be 

 given, beginning with the lowest. 



3. General characters of Radiata. 



6. The RADIATA possess many points of affinity with the Vegetable king- 

 dom ; and of these, the circular arrangement of their parts is one of the most 

 evident. Many species of Sea-Anemone, for instance, present an appearance 

 so much resembling that of various composite blossoms, as to have been com- 

 monly termed Animal-flowers, a designation to which they further seem 

 entitled, from the small amount of sensibility they manifest, and the evident 

 influence of light upon their opening and closing. But it is in the tendency to 

 the production of compound fabrics, each containing a number of individu- 

 als, which have the power of existing independently, but which are to a cer- 

 tain degree connected with one another, that we recognise the greatest affinity 

 in structure, between this group and the Vegetable kingdom. Every tree is 

 made up of a large number of buds, which are composed of leaves arranged 

 round a common axis ; each bud has the power of preserving its own life, 

 and of reproducing the original structure, when removed from the parent stem, 

 if placed in circumstances favourable to its growth ; and yet all are connected 

 in the growing tree, by a system of vessels, which forms a communication 

 between them. This is precisely the nature of the structures formed by the 

 animals of that class, which may be regarded as the most characteristic of the 

 Radiate group. Every mass of Coral is the skeleton of a compound animal, 

 consisting of a number of polypes, connected together by a soft flesh, in which 

 vessels are channelled out ; these polypes are capable of existing separately, 

 since each one, when removed from the rest, can in time produce a massive 

 compound fabric, like that of its parent ; but they all contribute to the main- 

 tenance of the composite structure, so long as they are in connection with it. 

 In some instances the skeleton is stony, and is formed by the deposition of 



