AMCEBA 135 



the chromatin particles, now separated into two groups, of 

 which one travels towards each pole of the nucleus. After 

 the separation of the chromatin groups, the two nuclei divide 

 to form four, and division of the cell-body follows. Indica- 

 tions of mitosis have been described in Amxba proteus and 

 A. verrucosa. In view of this conflicting evidence, it cannot 

 be decided whether amitotic division is of normal occurrence 

 or not in Amoebae. Some authors maintain that when once 

 an amitotic division has taken place the two resulting nuclei 

 are incapable of further division, and on this view mitotic 

 division would be the rule, amitotic the exception in Amoebae. 

 But there is no evidence of the truth of the statement, and 

 the most that can be asserted is that both mitotic and 

 amitotic division have been observed. In some Rhizopods, 

 which diflFer only from Amoebae in the fact that they form 

 a test or shell for themselves, mitotic division appears to be 

 the rule. (Euglypha, Arceila.) 



Occasionally an Amoeba is seen to withdraw its pseudopods, 

 to become spherical, and surround itself with a firm coat, 

 and so pass into a resting-stage, or as is generally said, to 

 encyst itself. After a time the cyst wall is absorbed, and 

 pseudopodial movement resumed, so that there is no necessary 

 connection between encystment and reproduction. It has 

 been stated, however, that encystment is sometimes accom- 

 panied by the breaking up of the nucleus into small fragments, 

 which become surrounded with cytoplasm, and are set free 

 as minute reproductive bodies called spores. It is further 

 said of one species, Faramceba eilhardi, that the spores emerge 

 from the cyst as minute actively swimming bodies, each pro- 

 vided with a nucleus and a pair of long vibratile flagella or 

 cilia. Eventually the spores are said to lose their flagella 

 to become amoeboid, and grow into new Amcfibae. But the 

 observations on which these statements are founded are not 

 entirely satisfactory, and it must remain doubtful for the 

 present whether true Amoebae ever reproduce themselves by 

 spore formation. Nor is there any evidence to show that 

 conjugation — i.e. the fusion of two individuals, or at any rate 

 the fusion of nuclear matter derived from two separate 

 individuals — is either a necessary or even an occasional pre- 

 lude to reproduction in Amcebse. 



Amoebae and their allies, distinguished from other Protozoa 



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