CHAPTER XLIII 

 MOVEMENT, ENVIRONMENT. 



Physiology of Movement. 



1. Review the phenomena of amoeboid movement (I, F, etc.). 



2. Review ciliary action (V). 



3. Muscle-nerve physiology (selected experiments from Section I) . 



Responses of Organisms to Environment, Regeneration. 



The functional unit of the nervous system in multicellular animals 

 is the reflex arc. This consists in its simplest form of a receptor, 

 an afferent nerve, an efferent nerve, and an effector. In verte- 

 brates, for example, the receptor is a sense organ like the eye, 

 which is affected more readily by a certain stimulus than are the 

 other sense organs. The change wrought in this sense organ by 

 the stimulus affects the afferent nerve in such a way that a nervous 

 impulse is initiated and passes along the afferent nerve to the 

 central nervous system. Usually the impulse passes over an inter- 

 mediate neurone before it reaches the efferent neurone. From the 

 efferent neurone the impulse passes to some gland, or muscle, the 

 effector, which acts in its own characteristic fashion. 



A. Experiments from Section III will be selected to illustrate 

 reflex arcs and the functions of the central nervous system of the 

 frog as an example of a vertebrate, and from Section V to illustrate 

 the action of receptors. 



B. Invertebrates are more stereotyped in their reactions, and 

 their responses to external stimuli are often constant and invari- 

 able. To these responses has been applied the term "tropisms" 

 (also " taxes"). (Consult Loeb " Forced Movements, Tropisms, 

 and Animal Conduct"). 



The material to be studied is the flat worm, Planaria maculata. 

 Note methods of locomotion (1) on flat surface under water, (2) on 

 the surface film, (3) in air. Does the animal ever swim freely? 

 Is the entire ventral surface in contact with the substrate during 



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