Chap. III.] OF SENSE ORGANS. 69 



ating from the viscera — are undoubtedly very important 

 in relation to animal life generally. In part, they have 

 the effect of causing contractions of related muscular por- 

 tions of the viscera — as when the presence and pressure 

 of food in certain portions of the alimentary canal excites 

 — it may be through local ganglia — contractions by which 

 the food is propelled farther on. In part, however, they 

 act upon the principal nerve ganglia — those constituting 

 the brain — in such a way as to excite the external sense- 

 organs with which they are connected to a higher order of 

 activity. Visceral impressions of one kind may cause an 

 animal more eagerly to pursue prey, whilst those of 

 another sort may tend to an increased alacrity in dis- 

 covering a mate. In these, and in many other instances, 

 internal impressions, reaching the cerebral ganglia, would 

 seem to excite a higher receptivity for certain kinds of 

 external impressions and a corresponding increased readi- 

 ness to respond on the part cf the moving organs whose 

 activity is related to such conjoined impressions and 

 promptings. 



With the second set of impressions, those of the so- 

 called ' muscular sense,' we have at present nothing to 

 do. They differ altogether from others, whether of ex- 

 ternal or of internal origin, by the fact that they follow or 

 accompany movements whose intensity they are supposed 

 to measure, and do not of themselves incite movements. 

 Granting that such impressions have a real existence, 

 it is obvious we can know nothing about them among 

 Invertebrate Animals, since they have only a subjective 

 existence and do not of themselves alone lead to move- 

 ments. Our only knowledge of such impressions, as 

 subjective states, must be derived from our own sensations 

 together with what other fellow-men are able to describe. 



