CHAI-. XXVT.l VOLUNTARY MOVEMENTS. 585 



ingoing Impressions of all kinds converge from various 

 parts of the body : here they come into relation with one 

 another in various ways, and conjointly give rise to nerve 

 actions, which have for their subjective correlatives all the 

 Sensations and Perceptions, all the Intellectual, and all 

 the Emotional Processes which the individual is capable of 

 experiencing. From these terminal and complexly related 

 ' end-stations ' for ingoing currents, and from certain 

 annexes in connection therewith, outgoing currents issue, 

 which rouse in definite ways the activity of the highest 

 ' motor centres ' (the Corpora Striata and Cerebellum), 

 and through them evoke the properly adjusted activity of 

 lower motor combinations, so as to give rise to any Move- 

 ments that are ' desired,' or which are accustomed to 

 appear in response to particular Sensations or Ideas. 



The plan on which Nerve Centres generally are con- 

 structed, of whatsoever grade, makes it essential that the 

 stimulus which awakens the activity of a ' motor ' ganglion 

 or centre shall come to it through connecting fibres from 

 a ' sensory ' ganglion, centre, or knot of cells that is, 

 from cells which stand in immediate relation with ingoing 

 fibres (see p. 26). 



If we turn to the very simple nervous system of a Slug 

 (fig. 27) we find two upper Sensory Ganglia, connected by 

 distinct ' commissures ' with two conjoined Motor Ganglia. 

 It can scarcely be doubted that stimuli (as sequences of 

 the nervous processes concerned with Sensations) are accus- 

 tomed to pass from these Sensory Ganglia along the ' com- 

 missural ' fibres uniting them with the Motor Ganglia, and 

 that, in accordance with their different origins or starting- 

 points, these stimuli may cause the latter Ganglia to 

 evoke distinctive muscular contractions in various parts of 

 the body. Could we galvanize separately the several sensory 

 ends of these ' internuncial ' fibres we should doubtless 



