REPRODUCTION 



amoeba, and is always posterior as the animal moves. Another 



kind of fission, known as multiple fission or spore formation, 



takes place at times. The nucleus divides till a very large number 



of small nuclei has been formed. These pass to the surface of the 



cytoplasm, which gathers into a little mass around each of them 



to make spores, which break free, feed 



for a week, and then encyst. After a 



week or more they emerge, feed and 



grow, and then encyst again for ap to a 



month. This process is repeated, and 



after three months the amoebae, which 



are now seven times the diameter of the 



original spores, emerge from the cysts 



and grow rapidly to the adult size. In 



other species the spores are formed in a 



cyst (Fig. 12). The young form is of 



various types, but, contrary to what 



is sometimes stated, is never, so far as 



is known, flagellate. 



Syngamy has not yet been proved to 

 occur in Amceha proteus. The animal 

 does, however, occasionally undergo a 

 process known as plastogamy, in which 

 the cytoplasm of several individuals 

 fuses, forming a single mass which 

 contains several nuclei. Such a mass is 

 known as a plasmodium. Quite another 

 kind of multi-nucleate body is found ^^' ln~Aniaeba^ —^Ait^T 



Scheel. 



A, 



in certain species of Amceha and in the 

 amoeba-like animals known as Pelomyxa, 

 where two or more nuclei are formed 

 by the division of a single nucleus, 

 giving a coenocyte or symplast. Plas- 

 modia and symplasts differ only in their 

 mode of formation and are collectively known as syncytia. 



Amaba encysted ; B, section of 

 a cyst in which numerous nuclei 

 have been formed, more highly 

 magnified ; C, surface view of a 

 ripe cyst in which the spores 

 are beginning to separate and 

 the cyst wall to break up ; D, 

 a single spore highly magnified. 



AMCEBA AND ITS SURROUNDINGS 



We have studied Amceba as an example of apparent simpHcity 

 in organisation. That is not to say that it is primitive in the 

 sense in which that term is used by zoologists ; it is unhkely that 



