THE PROTOZOA 223 



microscope it looks like an irregular, colorless particle of ani- 

 mated jelly. Two regions are distinguishable in its body, the 

 ectosarc and the endosarc. The ectosarc (Fig. 133, 3) is the 

 outer colorless layer. It is firmer than the endosarc and is free 

 from granules. The endosarc is the large central mass of granu- 

 lar protoplasm. Within it lies the nucleus (Fig. 133, /), which 

 is difficult to find in living Ameba, but can easily be made out 

 in animals that have been properly killed and stained. A con- 

 tractile vacuole may be seen in favorable snecimens. 



FOOD. The food of Ameba consists of very small aquatic 

 plants and animals. The ingestion or taking in of food occurs 

 without the aid of a mouth. Food may be engulfed at any point 

 on the surface of the body, but it is usually taken in at what may 

 be called the temporary anterior end ; that is, the part of the 

 body toward the direction of locomotion. A small amount of 

 water is taken in with the food, so that there is formed a vacuole 

 whose contents consist of a particle of nutritive material sus- 

 pended in water. The whole process of food taking occupies 

 one or more minutes, depending on the character of the food. 



PHYSIOLOGICAL ACTIVITIES. - - The various physiological ac- 

 tivities, such as digestion, assimilation, excretion, respiration, 

 and reactions to stimuli, are similar to those in Paramecium. 



LOCOMOTION. - - Ameba has no cilia such as cover the body of 

 Paramecium, and moves in an entirely different way. The 

 ectosarc bulges out into a fingerlike projection, the pseudopo- 

 dium (Fig. 133, j), and then the endosarc flows into it. In this 

 way the entire animal glides slowly along. There is, however, 

 no permanent anterior end. 



REPRODUCTION. - - Reproduction is by binary fission and by a 

 process known as sporulation. There is a limit with regard to 

 the size that may be attained by Ameba and when this limit is 

 reached, the animal divides into two parts. First, the nucleus 

 divides; then the animal elongates, a constriction appears near 

 the center, and division into two daughter cells finally takes 

 place. 



