14 



Contractility in medusa Locomotive power Pieces swim 



after being cut off from it. 



Universality of contractility Experiments on the locust Mus- 

 cular contractility not essentially different from that 

 of cellular tissue, with or without fibres Both may be 

 controlled by the will, and both survive in separated por- 

 tions of the animal Effects of galvanism False doctrine 

 of nervous fluid Muscles not necessary to locomotion 

 Nerves not always necessary to stimulate muscular motion 

 Examples from frogs and man. 



Contractility the common cause of motion in animals Com- 

 mon to all, or nearly all parts of them Cannot act with- 

 out a stimulant exciting irritability Irritability different 

 in different parts, requiring different stimulants. 



Hence all the motions of life are caused by stimulants 

 Folly of Grahamism. 



LECTURE VIII. 



Of Ciliary Movement Tonicity the Masticatory Apparatus 

 the Alimentary Canal and Muscular System. 



Wide diffusion of CILIA throughout the animal chain. 



Mode in which Polypi take their prey. 



Motions of the gemmules of sponge; of the infusory ani- 

 malcules; of pieces cut from the breathing organs of the 

 muscle shell-fish. 



Probable presence of cilia in the lungs and alimentary canal 

 of the more perfect animals. 



Cilia of certain plants The Chara.Hispida Vegetable cir- 

 culation Ciliary movements a result of contractility. 



Definition of TONE and ToNicrrr- a form of contractility. 



The contraction of contractile parts continues for a time after 

 the removal of the stimulant exciting it. Illustrations. 

 The motion of the leaves of the Dionoea or fly-trap. Na- 

 ture of fainting fits. Mexican sacrifices. This is one of 

 the principles involved in the theory of Habit. Exam- 

 ples of Tonicity. 

 Importance of tone in promoting vital functions. Effects 



