248 FUNCTIONS OF THE NERVOUS SYSTEM. 



should an impression made on one part be propagated by these to a distance ? 

 And how can that consciousness and will, which are one in each individual, 

 exist in so many unconnected particles ? If, then, we allow any sensibility, 

 consciousness, and voluntary power, to the beings of this group of Acrita 

 to deny which would be in effect to exclude ihem from the Animal Kingdom 

 we must regard these faculties as associated with nervous filaments, of such 

 delicacy as to elude our means of research. When the general softness of 

 the textures, and the laxity of structure that characterizes the nervous fibres, 

 in the lowest animals in which they can be traced, are kept in view, little 

 difficulty need be felt in accounting for their apparent absence. The case is 

 very different from that of Vegetable structure ; the greater consistency of 

 which enables us to place much more reliance upon the negative evidence 

 afforded by anatomical research. 



312. The correctness of this view (which has been here dwelt on the longer, 

 because it involves a fundamental question in Nervous Physiology), is borne 

 out by the fact, that, in those members of the group whose size and consist- 

 ency allow their structures to be sufficiently examined, a definite nervous 

 system has been detected ; in the position which it might, priori, be ex- 

 pected to occupy, according to the type of the individual. Thus, in the large 

 fleshy isolated polype, commonly known as the Sea-Anemone (Jlctinia), a 

 nervous ring has been discovered, surrounding the mouth as in other Radiata, 

 and sending off branches to the tentacula, with a minute ganglionic enlarge- 

 ment at the base of each. In the higher Radiata, as the Star-Fish, the nerv- 

 ous system has the same regular form as that which prevails through the 

 other organs. The mouth is surrounded by a filamentous ring, which presents 

 a regular series of ganglionic enlargements, one of them corresponding with 

 each segment of the body. From every one of these, a branch is transmitted 

 to the corresponding ray ; and two smaller ones proceed to the viscera included 

 in the central disk. 



313. The POLYPIFERA being the lowest of the Radiated classes, in which 

 there is a regularly-organized digestive apparatus, and which perform move- 

 ments of a character ascribable only to a Nervous System, it will be desir- 

 able to inquire a little more particularly into the phenomena they exhibit, and 

 the degree in which these necessarily involve the possession of the higher 

 mental endowments. In this inquiry we shall refer principally to the little 

 Hydra, or fresh-water Polype; the habits of which are better known than 

 those of any other species. Although no nervous filaments have been de- 

 tected in this, we have a right to infer their presence for the reasons already 

 given; and they probably form a ring around the mouth, as in the Actinia, 

 sending filaments to the tentacula. This interesting little being may be re- 

 garded as essentially a stomach; and the orifice of this is provided with 

 tentacula, which contract when irritated by the touch of any adjacent body, 

 and endeavour to draw it towards the entrance Now, the action in the Hu- 

 man body, to which this is most allied, is evidently that of the muscles of 

 Deglutition ; which lay hold, as it were, of the food that has been conveyed 

 to the fauces, and carry it into the stomach. These muscles are called into 

 action, not by an effort of the will, but by the contact of the food with the 

 lining membrane of the pharynx. This impression is propagated by the 

 glosso-pharyngeal nerve to the medulla oblongata. where a respondent motor 

 impulse is excited, which is transmitted through the pharyngeal branches of 

 the par vagum to the muscles of deglutition, and causes their contraction. 

 This phenomenon will be more fully examined hereafter ; it is here adduced 

 simply as an instance of the important class of re/lex movements, which are 

 independent of the brain (though, to a certain extent, controlled by it), which 

 are altogether involuntary, and which do not necessarily involve the produc- 



