STOMATO-GASTRIC SYSTEM OF INVERTEBRATA. 263 



the principal centre of the reflex actions of those nerves, which correspond to 

 the third branch of the fifth pair, to the glosso-pharyngeal, and to the gastric 

 portion of the par vagum, in Vertebrata; whilst the branches which connect 

 them with the cephalic ganglia, bring these nerves more or less under the 

 influence of the latter. The lateral ganglia seem more analogous to the 

 centres of the Sympathetic system in Vertebrata; especially in the connection 

 of their branches with all the other systems of nerves; and in the share 

 which they have in the formation of the co?liac ganglia. This view of the 

 relative functions of these two divisions of the stomato-gastric system, is 

 strengthened by the fact, that the connection between the Sympathetic system 

 of Fishes and the Par Vagum is much more intimate than in the higher 

 Vertebrata; although, even in the latter, as will be shown hereafter, it is by no 

 means so slight as it appears.* 



335. Upon taking a general review of the facts which have been stated, 

 and of the inferences which have been erected upon them, we perceive that 

 a gradual elevation may be traced, in the character of the actions to which the 

 Nervous System is subservient, as we ascend from the lower to the higher 

 parts of the Animal Scale. In the Radiata and lower Mollusca, in which no 

 organs of special sensation exist, all, or nearly all, of the movements which 

 are witnessed, may be legitimately regarded as simply reflex in their character ; 

 being analogous to those, which are unquestionably so in the higher animals ; 

 and being performed by the instrumentality of a nervous apparatus, that 

 seems to have little else than an intermmcial purpose. But when, as in 

 the higher Mollusca and in nearly all the Articulata, we meet with distinct 

 organs of special sensation, it becomes evident that the consciousness of the 

 animal must be concerned in the direction of its actions; since no impressions 

 upon these organs (the eyes, for example) can exert any motor influence on 

 the muscles, except by producing sensations ; that is, if we may apply to 

 the lower tribes the laws deduced from the study of the higher. Whilst, 

 therefore, a large proportion of the actions of the higher Invertebrata still 

 continues to be reflex (as we have especially seen in the Articulata), a new 

 group is superadded to these; and this, consisting of actions, which are 

 directly stimulated by sensations, and in which no Reasoning powers nor 

 Will appear to have any direct participation, may be termed consensual. 

 They require, as their instruments, a set of ganglia to receive the trunks which 

 originate in the organs of sense, and to issue motor nerves to the several parts 

 of the body. These last are distributed along with the trunks, which are 

 connected with the ganglia belonging to each particular organ ; thus the legs 

 and wings of an Insect appear to derive their motor nerves, partly from the 

 ganglia of the ventral cord, which minister to their reflex actions, and partly 

 from the cephalic ganglia, which seem to harmonize, to control, and even to 

 antagonize, the influence of the former. In like manner, the parts of the 

 body, which are capable of receiving sensory impressions, appear to have a 

 double connection ; one with the ganglia of the ventral cord, for the purpose 

 of conveying thither those impressions which are destined to excite reflex 

 actions; and the other with the cephalic ganglia, in order to originate sensa- 

 tions. Of this double system of nerves and ganglia, the one connected solely 



* The view given above of the comparative structure and offices of the Nervous System, 

 in the Invertebrated animals, is chiefly abridged from the Author's Prize Thesis on this 

 subject; in which additional details will be found, as well as many other illustrative figures 

 and references to authorities. He has there, also, discussed the physiological explanation 

 which had been previously given of the double nervous cord of the Articulata ; and having 

 shown that it is neither consistent with itself, nor capable of being applied to the other 

 Invertebrata, he has deemed it unnecessary to complicate the present sketch by introducing it. 



