ADDRESS. 7 



Let us observe our Amoeba a little closer. Lite all living beings, it 

 must be nourished. It cannot grow as a crystal would grow by accumu- 

 lating on its surface molecule after molecule of matter. It must feed. It 

 must take into its substance the necessary nutriment ; it must assimilate 

 this nutriment, and convert it into the material of which it is itself 

 composed. 



If we seek, however, for a mouth by which the nutriment can 

 enter into its body, or a stomach by which this nutriment can be digested, 

 we seek in vain. Yet watch it for a moment as it lies in a drop of water 

 beneath our microscope. Some living denizen of the same drop is in its 

 neighbourhood, and its presence exerts on the protoplasm of the Amoeba 

 a special stimulus which gives rise to the movements necessary for the 

 prehension of nutriment. A stream of protoplasm instantly runs away 

 from the body of the Amoeba towards the destined prey, envelopes it in 

 its current, and then flows back with it to the central protoplasm, where 

 it sinks deeper and deeper into the soft yielding mass, and becomes 

 dissolved, digested, and assimilated in order that it may increase the size 

 and restore the energy of its captor. 



But again, like all living things, Amoeba must multiply itself, and so 

 after attaining a certain size its nucleus divides into two halves, and then 

 the surrounding protoplasm becomes similarly cleft, each half retaining 

 one half of the original nucleus. The two new nucleated masses which 

 thus arise now lead an independent life, assimilate nutriment, and attain 

 the size and characters of the parent. 



"We have just seen that in the body of an Amoeba we have the type of 

 a cell. Now both the fresh waters and the sea contain many living beings 

 besides Amoeba which never pass beyond the condition of a simple cell. 

 Many of these, instead of emitting the broad lobe-like pseudopodia of 

 Amoeba, have the faculty of sending out long thin threads of protoplasm, 

 which they can again retract, and by the aid of which they capture their 

 prey or move from place to place. Simple structureless protoplasm as 

 they are, many of them fashion for themselves an outer membranous or 

 calcareous case, often of symmetrical form and elaborate ornamentation, 

 or construct a silicious skeleton of radiating spicula, or crystal clear 

 concentric spheres of exquisite symmetry and beauty. 



Some move about by the aid of a flagellum, or long whip-like pro- 

 jection of their bodies, by which they lash the surrounding waters, and 

 which, unlike the pseudopodia of Amoeba, cannot, during active life, be 

 withdrawn into the general protoplasm of the body ; while among many 



has seen a relation between these and the cilia on the swarm spores of Vaucheria, 

 where each cilium seems to be supported by a rodlet. That this condition of the 

 cortical layer, however, is not a general feature of cell protoplasm, is certain ; it 

 is but a special case of structural differentiation. Indeed, the complex structure 

 which has been detected in the nucleus and in the surrounding cell-protoplasm 

 ■can scarcely be otherwise regarded than as an expression of an early differentiation 

 in the structure of the cell, and not, as has been maintained, an ultimate or 

 ' plastidular ' condition of protoplasm. 



