CHAPTER II 



CILIARY ACTIVITY, AMCEBOID MOTION AND COLOUR RESPONSE 



In the previous chapter we have considered a form of response 

 which has several advantages for experimental treatment. The 

 activity of skeletal muscle is not spontaneous, it can be made 

 accessible at will. Further, muscular tissue can be obtained in 

 sufficient bulk to facilitate very considerably the measurement 

 of the energy changes which accompany its activity. On the 

 other hand; all that we know of the muscular mechanism is 

 of a statistical nature. In the case of ciliary, amoeboid, and 

 chromatophore movements, however, it is possible to make 

 direct observations on individual cellular units. To these 

 forms of response, which are more conveniently studied in the 

 lower organisms, we shall now turn, taking first of all ciliary 

 activity. Of this, our knowledge has been lately advanced by 

 the extensive investigations of Gray (i 922-1 924), which will 

 form the basis of the present treatment. 



Ciliary Motion. — For a clear appreciation of the issues 

 raised by a consideration of the mechanism of ciliary motion, 

 a few remarks must be introduced concerning the contractile 

 rhythm of the ciliated cell. Favourable material for observa- 

 tions of this kind are afforded by the gills of the common 

 mussel Mytilns. The face and sides of each filament are 

 respectively lined with frontal and lateral ciliated cells, whose 

 movement maintains an efficient stream of water and mucus 

 (see Chapter V) easily detected by the naked eye if a little car- 

 mine is added to the medium. Microscopic observation shows 

 that the maintenance of these currents in a definite direction 

 is due to the characteristic manner in which the cilium moves. 

 The movement of a single cilium is divisible into two phases, 

 a very rapid forward or effective stroke, and a slower backward 



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