THE AMCEBA THE ASC1DIAN. 83 



causes, and the mechanism of movement in plants. 

 In animals we see movement result from the action 

 of the organism as a whole, or from the action of 

 parts of it, and this is one of the most constant 

 facts seen in the lowest and highest grades of 

 animals. The movements of amcebse and other 

 protozoa have been often observed. The body of 

 the amoeba is less firm than jelly, yet it has the 

 power of moving from place to place. At first 

 appearing as a shapeless mass, it may rapidly throw 

 out filaments, or projections, which may again be 

 retracted into the mass of the amoeba. All parts 

 of this mass appear to be alike, and similarly 

 endued with contractile powers. These filmy 

 patches glide about although the eye can detect 

 no differentiation of their parts, and there is no 

 special mechanism for producing force, apart from 

 the portions that produce movements. 



In such animals there is no differentiation into 

 force-producing parts, and motor-organs ; every part 

 of the body can perform all the functions of the 

 whole organism: thus it is seen that the amoeba 

 has an organization lower than that of the Oxalis 

 and Mimosa piidica, which have special motor- 

 organs. 



In the ascidian there is a mechanism for the 

 production of motor-power, and a contractile appa- 

 ratus as a moving instrument. " The nervous appa- 

 ratus consists of a central ganglion, Fig. 3 (c), con- 

 nected with the periphery by two sets of nerve- 

 filaments. One set is distributed to a part of the 

 integumentary surface capable of receiving and 



