in their Structure and Functions. 1 25 



of respiration, and both are unconnected with the faculties of 

 perception and volition. It therefore appears that the Des- 

 niodium gyrans is endued with something like respiratory 

 nerves, upon the agency of which the motions of its leaves, 

 which resemble the contractions of the diaphragm, entirely 

 depend. 



The motions of the animal body are divided into volun- 

 tary and involuntary. Now, it appears that volition, or the 

 act of the mind which forms the will, is the chief stimulus of 

 the nerves distributed to the muscles of voluntary motion ; 

 for instance, if we wish to move a limb in a certain direction, 

 provided the nerves and muscles belonging to it are in a sound 

 state, it is immediately moved. In this case, a certain state 

 of the brain is induced by volition : this is conveyed to the 

 nerves, which, acting on the muscles, cause them to contract, 

 and to move the limb. But the nerves which place the 

 muscles under the guidance of the will can act upon and 

 produce contractions in these muscles, without themselves 

 being operated upon by volition. This is proved by the act 

 of deglutition in new-born infants, which depends on certain 

 muscular motions. These motions cannot, of course, be re- 

 garded as voluntary ; because there must always be present 

 in the mind a motive before voUtion can be exercised ; and 

 since there does not exist in infancy any mental feelings 

 whatever, we are bound to conclude that deglutition at this 

 period of life is an involuntary but a spontaneous act. That 

 the muscles of deglutition, during infancy, act in consequence 

 of the stimulating power of the motive nerves, there can be 

 no doubt ; because they perform their office independently 

 of all external circumstances, and because they cease to per- 

 form it if the nerves ramified upon them be divided, or dis- 

 abled by disease. It is clear, from what has been said, that 

 the motive nerves can act on the muscular fibre, whether they 

 themselves be acted on by volition or not. In the former 

 case, i. e. when acted on by volition, they produce what is 

 termed voluntary motion ; in the latter case, i. e. when not 

 acted on by volition, they give rise to spontaneous motions. 

 It is well known that the pistil of the tiger lily will bend, 

 first towards one stamen, and then towards another, until it 

 has inclined towards them all. Each stamen of the 5axi- 

 fraga* will in regular succession approach the pistil, and 

 as soon as it has shed its pollen over it, it retires, and 

 gives place to another. These movements do not depend 



* Which, or every species ? Parnassia palustris also instances the same 

 phenomenon. — J,D, . 



