GENERAL CHARACTERS OF RADIATA. 439 



we may observe a progressive removal from the Plant-like con- 

 dition, in which the simplest of these beings exist. This 

 elevation is manifested in two ways ; in the gradual complica- 

 tion of the nutritive system ; and in the evolution of those 

 powers of sensation and independent motion, which differ from 

 any faculties exhibited by vegetables. We shall notice that, 

 whilst in Sponges the tissue is nourished simply by the intro- 

 duction of the surrounding fluid into the channels of its substance 

 a mode differing but little from the absorption by the roots 

 and general surface of plants the Polypes are furnished with a 

 regular stomach, and with prehensile appendages for conveying 

 into it solid nutriment, on which it exercises a most powerful 

 digestion. In the larger and more solid Echinodermata, this 

 complexity of organisation becomes more distinct ; the tissues, 

 instead of consisting of soft and nearly homogeneous membrane, 

 exhibit all the varieties of nerve and muscle, tendon and liga- 

 ment, distinct vessels and cartilaginous or even bony skeletons. 

 The stomach, instead of being a simple bag into which everything 

 is introduced that comes within the animal's reach, whether it 

 be digestible or not, is but the commencement of a regular ali- 

 mentary canal, furnished with a set of teeth at its entrance for 

 the reduction of the food, and with glandular appendages for the 

 secretion of the fluids required in the digestive process. And 

 we even find distinct organs appropriated to the aeration of the 

 blood, which sometimes present a very complex arrangement. 

 Now it is remarkable that, with so great an advance in the 

 organisation of the nutritive apparatus, we should find the 

 locomotive and sensorial powers very little developed even in 

 the highest ; so that in this respect they are far surpassed by 

 the simpler Articulata, whose general organisation is much 

 inferior. But it must be remembered that the perfection of the 

 locomotive apparatus is the distinguishing or typical character of 

 the Articulata, and that everything is made subservient to it ; 

 whilst conformity with the Plant-like condition seems to be 

 equally the typical character of the Radiata ; being only de- 

 parted from in those higher forms, which conduct us towards 

 other groups. 



