126 GENERAL BIOLOGY 



ing, there are two methods of division. The so-called simple binary or 

 amitotic, just mentioned, and a process known as speculation. There 

 have been a few instances reported where the animal formed definite 

 mitotic figures. Very few investigators have observed sporulation. 

 "This latter process lasted from two and one-half to three months ; the 

 pseudopodia were first drawn in, and the animal became spherical. A 

 three-layered cyst was then secreted. The Amoeba rotated within these 

 for several days after which all movement ceased. The nucleus divided 

 until there were twenty or thirty nuclei present, arranged near the sur- 

 face. Continued division resulted in an increase of nuclei from five 

 hundred to six hundred. Walls now appeared at the periphery, cutting 

 off the nuclei, each with a small amount of cytoplasm. The wall of the 

 cyst became soft, broken, and allowed the small amoeba to escape. Hun- 

 dreds of these amaebulae or pseudo-podiospores, as they are sometimes 

 called, broke out at one time. They became recognizable as Amoeba 

 proteus in from two and one-half to three weeks. No reason could be 

 discovered for sporulation, although experiments were conducted in 

 which specimens were starved, were given an excess of food, were al- 

 lowed to dessicate, and were transferred to water from different locali- 

 ties ; none of these resulted in encystment and sporulation." 



However, whichever way the animal may divide it is simply a mat- 

 ter of growth before it is ready to divide again. We have here the 

 interesting fact confronting us that these little single-celled animals are 

 practically immortal. That is, they do not die. One may kill them by 

 boiling and in other ways ; but, left to themselves, they will continue 

 until they have reached their limit of adultship when they divide, each 

 individual becoming two new and separate animals. 



It is important that the fact be grasped that in these little unicellu- 

 lar animals a parent does not give birth to its offspring. The parent 

 itself becomes the offspring. That is, there are no ancestors. Each and 

 every animal carries its complete and total ancestry with it. 



BEHAVIOR 



The way in which an animal reacts to a stimulus is called its be- 

 havior; and when that behavior has not been learned, but comes forth 

 without consciousness on the part of the animal, yet is protective to the 

 animal, such behavior or reaction is called instinct. In these lower one- 

 celled animals two words are used in discussing behavior and instincts. 

 These are tropisms or taxis, which merely mean a movement of some 

 kind. To these words one adds the generic name of the stimulating 

 cause, using the word positive and negative to explain one's meaning. 

 For example, there are usually eight tropisms or taxis mentioned : 



(1) Thigmotropism, meaning a reaction to contact of some kind; 



(2) Chemotropism, meaning a reaction to a chemical; 



