AMCEBA PROTEUS 



333 



The amcsba draws in its pseudopodia and assumes a spherical shape at a temperature of 35' C. If the 

 temperature be raised to 40° C. it dies. Under unfavourable circumstances, such as drought, the ectoplasm secretes 

 a thin hyaline case, and the amcEba becomes encysted and dormant, in which condition it is carried by the wind or 

 other means to various localities. 



The amoeba is invested with practically universal powers, and furnishes one of the most remarkable examples 

 known of the potentialities residing in rudimentary living matter. Thus any part of its substance may become a 

 stomach and digest its food, and any part of its body may throw off the waste products ; it has, however, neither 

 mouth nor anus. It feeds upon diatoms, desmids, spores of algas, and other vegetable matter, and occasionally on 

 animal matter, such as portions of rotifers and of Protozoa, notably Arcella. 



When the amoeba falls in with a microscopic alga or food particle, the protoplasm flows round it ; the ectoplasm 

 opening to receive it and closing behind it. It enters the endoplasm with a drop of water which constitutes the 

 food-vacuole, and is temporarily included in the body of the amoeba. The alga is slowly digested, its insoluble 

 proteids being converted into soluble and diffusible proteids, which pass into the substance of the endoplasm. It 



Fig. 68. 



Fig. 68. — Ama'ha pwteux as seen under varying conditions of size and shape (A to J), magnified from 400 to 800 diameters 

 (after Masterman, and Marshall and Hurst). 



A. Amoeba in the encysted state, composed mainly of granular and clear sarcode ; c, contractile vesicle ; d, nucleus. It con- 

 tains an oval-shaped diatom. 



B to J. Different shapes assumed by larger and smaller amoeba. In these figures the contractile vesicle is seen at c, the 

 nucleus at d, and the finger-like projections at e. The projections, sometimes designated pseudopodia, are for the most part 

 conicalin shape, as seen at C, D, E, F, G, H, and 1. They are caused by the animal voluntarily forging a part of its body outwards 

 from the centre centrifugally. They are retracted in an opposite direction or centripetally. They are not due to contractions ; if 

 they were, the projections would not be conical-shaped, but constricted where united to the body. In reality, they are produced 

 by an aggressive, streaming, rhythmic movement similar to what occurs in the plasmodium of the Mycetozoa and gromia already 

 described. 



At E, the body (a) of an amoeba is stretched over a large diatom (//). 



At J, the varying forms assumed by a small amoeba, at intervals of half-a-minute, are given. 



may be well to state that the proteids are themselves constituents of protoplasm. The amoeba, it is believed, cannot 

 digest carbo-hydrates or fats, and does not build up its protoplasm from lower chemical constituents. The 

 indigestible cellulose walls of alga and other intractable materials are extruded from the body. The amoeba 

 inhales oxygen and exhales carbonic acid, in which respect it resembles the higher animal forms. It has, however, 

 no branchiae, gills, or lungs ; its whole substance performing this important function. 



The reproduction of the amoeba is effected in the simplest manner possible. The nucleus, and with it the 

 sarcode of the body, divides into two. In this respect the process resembles the first step in the segmentation of 

 the impregnated ovum of the higher animals. There are, however (so far as known), no male and female elements, 

 and the animal is not hermaphrodite. The original individual becomes two separate entities, each of which, after 

 a short time, becomes as perfect as the parent, and so hfe is transmitted and continued in the most direct and effective 

 manner. The reproduction of the amoeba is fundamental and thorough-going. It does not require two separate 

 organs or individuals for its consummation. It is thought by some that the amoeba has not only the power of 

 dividing into two by binary fission, but that two amoebae can come together, coalesce, and conjugate to form one 

 individual. The process of conjugation, while not quite made out in the amoeba, certainly occurs in other low animal 

 forms, such as the Gregarines and Infusoria. The powers inhering in what is practically undifferentiated living 

 matter are at once striking and impressive. They bring us face to face with the eternal verities of matter and 



