714 



PROTOZOA. 



The lowest of the nucleated Protozoa are the Rhizopoda or root-foote 



animals, a name given to them on account of their manner of moving b 



means of root-like prolongations of the body. Th 



Tlie Ehizopoda. simplest of these Rhizopoda is the Amoeba, which ha 



been called the Proteus animalcule because of its constar 



changes of shape. These animalcules are to be found in most rain-watt 



puddles and in ponds, and when seen under the microscope might escap 



observation as mere specks of clear jelly-like matter, yet the careful observe 



will find that each such speck is capable of moving about and feeding, and 



indeed, can be proved to be living, carrying on all those functions which 



taken together, we designate as life. 



If a Proteus animalcule is magnified about three or four hundred times th 



following important points can be noted :— (1) It is naked, i.e., it has n 



cuticle or shell. (2) The surface layer of protoplasm 



The Amoeba. though not forming a skin, is clear and glassy, and com 



pletely envelops the more fluid and granular inner portioi 



of the Amceba. (3) Among these granules can be seen the nucleus am 



foreign particles, taken in as food, the remains of such particles, an( 



other bodies not understood. (4) Lastly, if thi 

 Amoeba is carefully watched, a round space, liki 

 a bubble, appears, increases in size, and thei 

 instantaneously disappears, forming again a 

 another spot. This is the contractile vesicl 

 which is thought to collect the waste product 

 of the body and to eject them when it con 

 tracts. 



The Amoeba is seen to change its shapi 

 slowly by protruding at certain points finger 

 like or knob-like processes which are callec 

 pseudopodia or make-believe feet. Its exceed 

 ingly slow movements over the surface of plant 

 or other submerged objects, or through thi 

 water, are all made by the extension of pseudo 

 podia in one direction and corresponding with 

 drawal on another side, the whole body seeminj 

 to flow on along its pseudopodia. If, in its course 

 it meets with minute plant cells suitable fo 

 food, it admits them into its body at any point, retains them within it for i 

 time, while it evidently assimilates some nourishment from them, and thei 

 flows on, the indigestible remains of its meal being left behind. Tht 

 manner in which the Amoeba breathes cannot be seen, but the fact that i 

 breathes is indisputable, for if the water in which AmoebiB are kept ii 

 deprived of its free oxygen, the assimilation of which is what is meant bj 

 breathing, the animals become rigid and lifeless. 



When, in consequence of the nourishment derived from the asaimilatei 

 particles, an Amoeba has grown to a certain limit, its shape becomes that o 

 a dumb-bell (Fig. 1, B), the nucleus divides into two, each end of the dumb 

 bell containing one of the new nuclei, the connecting part narrows more ant 

 more, and finally the two ends separate completely (Fig. 1, C), and eact 

 half (or "daughter") repeats the simple life activities of the original whoh 

 (or "mother"). These terms mother and daughter at first sight appeal 

 hardly justifiable, yet we now know that all reproductive processes, even ir 



Fig. 1.— A, B, C. 



A Proteus Animalculb i^Amcuba) 



in three fatages. 



