32 ACTION OF AUXETICS AND KINETICS 



rate of pulsation is diminished at 37 C. and the 

 vacuole is then larger than at the room temperature. 

 On death of the amoeba, the vacuole attains its 

 maximum size and remains motionless. In this 

 condition it may occupy as much as half the bulk 

 of the cell. At the same time, liquefaction of the 

 cytoplasm causes the amoeba to become spherical 

 with an apparent increase of the ectoplasm, due to 

 uniform bulging out of the periphery, and granular 

 matter may collect together into masses (fig. 10). 



Life-history. A variety of methods of multi- 

 plication has been described among the different 

 species of amoebae, and it is advisable briefly to 

 summarise these, particularly as the type on which 

 we are working appears to constitute a new species. 



(A) Binary Fission. In the free state, division 

 of the nucleus with or without karyokinesis is fol- 

 lowed by division of the amoeba into two approxi- 

 mately equal portions. This is the common mode 

 of reproduction which occurs when the amoebae 

 are under conditions suitable for their continued 

 growth. Rarer occurrences described as taking 

 place in various species are : (B) Multiple Fission, 

 the amoebae breaking up into several smaller ones. 

 (C) Resolution of the nucleus into chromidia 

 which form secondary nuclei, these in their turn 

 giving rise to internal buds which become dis- 

 charged as amoebulae. (D) Simple Budding or 

 Gemmation, a small portion of the body containing 

 nuclear matter being liberated, (E) Conjugation, 

 and, under special circumstances, the amoebae may 

 encyst and various changes take place within the 

 cysts, the nature of which has in many cases served 

 as a basis of classification. Thus (a) Encystment 



