The Protozoa 



125 



aquatic plants, other single-celled animals, bacteria, and various types 

 of animal and vegetable matter. 



It is of special interest to note that when food is taken by Amoeba 

 the animal really places its body around the food (Fig. 46). Experi- 

 ments with inorganic substances, such as a drop of chloroform in a 

 watch glass of water, have shown that the chloroform will take in sub- 

 stances like shellac, and paraffine and reject wood, glass, etc. It must 

 not be forgotten, however, that these substances, which are thus accepted 

 by the inorganic drop of liquid, are those which normally adhere to 

 chloroform. But with Amoebae the majority of food substances do not 

 adhere to the surface of the animal, and so again there is considerable 

 dissimilarity between the experiment and the actual facts in the case. 

 In digestion, the food vacuoles have been embedded in the 



endoplasm. The vacuole wall 

 secretes a fluid containing some 

 mineral acid, supposedly HC1. 

 This digestive fluid seems to 

 dissolve only proteid sub- 

 stances, and has no effects upon 

 fats and carbohydrates. Hofer 

 performed an interesting ex- 

 periment by cutting an Amoeba 

 in two parts after it had just 

 been well fed, and the part that 

 did not have the nucleus was 

 unable to digest food. 



A somewhat similar condi- 

 tion will be found a little later 

 in the study of the earthworm. If the earthworm is cut in two behind 

 certain segments, the forepart of the animal, which contains the impor- 

 tant organs, will regenerate a new tail, whereas the tail-part, which has 

 been cut off, will regenerate another tail. Such an animal has no mouth 

 and must consequently starve to death as it has no way of ingesting food. 

 After digestion has taken place in Amoeba, any indigestible particle 

 may be thrown out at almost any point on the surface of the animal. 

 These indigestible substances are probably heavier than the protoplasm 

 itself, so that this heavy portion sinks through the lower part of the 

 animal's body. Then, as the animal moves away, it leaves the indi- 

 gestible solid particle behind. 



There is no circulatory system proper in a one-celled animal, so that 

 after the food has been digested, it must be absorbed and passed into 

 the body substance proper of the animal. Here we come to a new term, 

 that of assimilation, which means that now that new food matter has 

 been digested and is within the body, there must be a rearrangement of 



Fig. 46. 



A, Amoeba encysted. 



B, Amoeba ingesting a plant, p, retracted pseudo- 

 podium; dt, plant (diatom) taken in as food. cv, 

 contractile vacuole; f.v., food vacuole; n, nucleus. 

 (After Leidy and Howes.) 



