78 



COMPAEATIVE ANATOMY. 



Fig. 22. An Amoeba figured at two 

 different moments during move- 

 ment, n Nucleus, i Ingested food. 

 Some vacuoles may also be noted. 



/ ..%' 



./..• 



'#, 



times tlie appearance of broad lobate prolongations (Fig. 22) 

 sepai-ated from one another by shallow depressions ; sometimes they 



flow out as delicate^ sometimes '.as 

 wedge-shaped, currents, which divide 

 in all kinds of ways at their periphery, 

 and so form ramified processes. These 

 changes are always within definite 

 limits of form in the various divisions, 

 so that the form of the pseudopodia 

 is the expression of the first differen- 

 tiation of a definite morphological 

 character of the protoplasm. The 

 pseudopodia characterise the Rhizo- 

 poda, the superficial protoplasm of 

 which is able to emit them in every 

 form of this group (Fig. 23). Neigh- 

 bouring pseudopodia can unite with 

 one another at any point and in various numbers (Fig. 23, x), or 

 may even become connected in a retiform manner. This character 



of the protoplasm is 

 / . .. / not affected by in- 



ternal differentiation 

 (skeletal organs, etc.). 

 It is the expression of 

 a stage in the lowest 

 living material when 

 it is not differentiated 

 at its periphery. 



When the outer- 

 most layer of the 

 body is hardened, 

 pseudopodia cannot 

 be formed at every 

 point. The chemico- 

 physical changes in 

 the peripheral parts 

 lead to the formation 

 of something unUke 

 the rest of the proto- 

 plasm, whichretainsits 

 indifferent character, 

 and indeed still gives signs of its power of movement, but is 

 restrained by the firmer cortical layer from any considerable exten- 

 sion of itself. . This stage is found in the G-regarinasj characters 

 which obtain in many of the AmCEbte exhibit intermediate steps 

 towards it. A firm homogeneous membrane sometimes delicately 

 striated, extends in these forms over the whole body, which is 

 formed by a single cell. It passes directly into the soft protoplasm, 

 and appears to be a cuticle differentiated from it. Like all cuticles, it 



'\'-'.\--.''^.'^--.'''--:-''S^'-X-.:'y^^^ 



i" 



Fig. 23. A Foraminifer (Rotalia) with extended 



pseudopodia, whicli pass through, the pores of the 



multiloculate shell. At x, several pseudopodia have 



united together. 



