13 



To this end, after briefly sketching the essential charac- 

 ters of an animal as distinguished from those of a plant, 

 and showing the extreme difficulty of drawing a boundary 

 line between the Vegetable and the Animal Kingdoms, the 

 author proceeded to describe the muscular and nervous 

 systems in general, they being the elementary parts of the 

 Locomotory Apparatus, as seen in the higher animals, and, 

 as far as can be judged from analogy, also the constituents, 

 in a diffused form, of the locomotory organs of those more 

 obscurely organised beings, winch stand at the bottom of 

 the animal scale, 



The muscular tissue of animals was shown to resemble 

 the contractile tissue in plants in contracting upon the 

 application of appropriate external stimuli; but to differ 

 from it, in being thrown into action also by stimuli ab intus, 

 conveyed to it through the nervous system. The spasmodic 

 contractions induced by an electric current, in an animal 

 recently dead, illustrated the former kind of movements, and 

 those consequent on volition, the latter. These were shown 

 to be effected by the motor nerves in connection with the 

 cephalic centre and with the medullary cord. 



That class of movements called " Reflex" was explained 

 to arise from the ganglia of the trunk. These ganglia, the 

 nervous centres of reflex action, are very numerous in the 

 lower animals, but, as we ascend in the animal scale, become 

 less important, in comparison with that portion of the 

 nervous system by which the will operates. 



The softness of the tissues of most of the Radiated 

 Animals, renders it very difficult to discern distinct traces 

 of a nervous system in them. In the Echinodermata, 

 however, it becomes very obvious. In the Star-fish, it is 

 exceedingly simple, forming a ring round the opening into 

 the digestive cavity. This circular cord connects five 

 ganglia, which give off the same number of trunks, one into 



