RHIZOPODA 3 



may be contracted, or the whole body protoplasm may flow 

 along after them, thus producing locomotion as well as constant 

 change of form. 



According to the experiments of Professor H. S. Jennings, 

 particles attached to the ectoplasm move forward on the upper 

 surface, disappear over the anterior edge, and, as the proto- 

 plasm flows along, appear again at the posterior end, to repeat 

 the circuit, showing that this locomotion is a sort of " rolling 

 process." 



Feeding. — As the amoeba flows or rolls along, if it comes in 

 contact with a particle which is unfit for food, it passes by or 

 over it, but if the particle is fit for food, it flows about and en- 

 velops it, and forms the so-called food vacuole. As this food 

 vacuole moves along the endoplasm, the digestible part of the 

 food disappears in digestion, while the indigestible portion is 

 left behind as the protoplasmic body moves along. 



Multiplication in the case of the Amwha is by binary division 

 or fission and by sporulation. This becomes necessary, since 

 the entire animal is but a single cell, and all the functions for 

 the whole animal must be performed by this one cell. Hence, 

 it must remain exceedingly small, so the nucleus, as well as the 

 body substance, divides into two halves, and two individuals 

 result. 



Encysting. — Under unfavorable environment, such as drouth, 

 the Amoeba contracts into a tiny sphere, becomes encysted or 

 encased in a horn-like membrane, and remains in a dormant 

 condition until favorable environment returns to it, or it is trans- 

 ported by the wind or carried bj' other animals — in the dirt 

 which has clung to them — to a favorable environment, where 

 it bursts its cyst and resumes active life. 



The Radiola'ria ;ire marine Rhizopoda which ha^-e their pseudopodia 

 arranged like rays. jNIany ot these forms possess a siUcious shell or skele- 

 ton, and myriads of these shells are found in rocks of various geologic 

 ages. One type reproduces by swarm spores, the original nucleus dividing 

 into hundreds of daughter-nuclei. 



The Foraminif era are Rhizopoda whose fresh-water forms have chitinous 

 or silicious coverings, while the typical members, which are marine, have 

 calcareous shells. ^\'hen the animal dies the shell sinks to the bottom of 

 the ocean. Such multitudes have existed that vast formations of chalk 

 or limestone rook have been made by their shells. The stone of the Pyra- 

 mids is said to be composed of fossil Foraminifera. 



