96 J. W. JKNKiNSON. 



III. The Life History. 



a. The Amoeba Stage. — The amoebse commonly arise by 

 the extrusion from the cyst of the whole of the multinucleate 

 contents, which then divide into two with the appearance of 

 pseudopodia. The process is repeated until the whole is divided 

 into uninucleate amoebae, which then encyst (Fig. A). 



There are often, however, modifications of this process. For 

 instance, the first division may take place during extrusion 

 from the cyst, in which single products of division may remain 

 behind and re-encyst (Fig. B) ; or the original amoeba may 

 divide into more than one at a time, or the second division 

 may begin before the first is completed. 



Less frequently the whole body breaks up simultaneously 

 into several pieces (Fig. C), assuming then the labyrinthine 

 appearance observed by Archer, the thickened nodes of the 

 meshwork being the separate energids of the protoplasmic body. 



The present author, however, only observed the streaming of 

 the protoplasm out of such cysts as that depicted in Fig. B, 

 not out of the Urococcus-like many-layered cysts, as seen by 

 Archer. 



It is probable that this streaming and simultaneous division 

 are due to favourable conditions of temperature, and so forth, 

 supervening on a prolonged period of unfavourable circum- 

 stances, during which the forces concerned have become much 

 intensified. At different stages of division, or even before the 

 first division has taken place, the amoebae ingest food particles, 

 mostly diatoms, and encyst themselves with these; the uni- 

 nucleate amoebse are only able, however, to ingest bacteria, or 

 very small green or blue-green Algae. More rarely they ingest 

 small pieces of Alga filaments, such as CEdogonium ; starch 

 grains they devour readily, and they will also take up grains 

 of sand or bits of decaying plants, though they soon egest these 

 again. 



After encystment there is, in all cases, a rapid multiplication 

 of the nuclei. In this condition they are generally found on 



