AMCEBA 1 19 



Amoeba proteus. During the winter the animal encysted 

 and its nucleus divided amitotically till a very large number 

 (some 600) of small nuclei had been formed. These passed 

 to the surface of the cytoplasm, which gathered into a 

 little mass around each of them. The cyst wall was now 

 dissolved and the little individuals or spores escaped as 

 small Amoebtz with fine, pointed pseudopodia unlike the 

 blunt processes of the adult, a residual mass of unused 

 cytoplasm being left behind. The young forms grew and 

 became transformed into adults. 



Conjugation has not been seen in Amoeba proteus. 1 The 



animal does, however, occasionally undergo a 

 Am(BtaBB? leate process known as plasmogamy, in which the 



cytoplasm of several individuals fuses, forming 

 a single mass which contains several nuclei. Such a mass 

 is known as a Plasmodium. The macrophages formed by 

 leucocytes (p. 100) are plasmodia. Quite another kind of 

 multinucleate body is found in certain Amceba-like animals 

 known as Pelomyxa, where two or more nuclei are formed 

 by the division of a single nucleus. These may be com- 

 pared with ccenocytes. 2 



Our survey of the life and structure of Amoeba has 



shown us that it must be regarded as an 

 the"ceii Theory. organism in no way inferior to the frog in its 



fundamental powers. It is irritable and auto- 

 matic, undergoes katabolism, contracts, conducts, does 

 chemical work, secretes and excretes, respires, incorporates 

 food, and reproduces. It differs from the frog only in the 

 extreme simplicity of its structural organisation, possessing 

 as it does no obvious permanent organs except the cyto- 

 plasm, nucleus, and contractile vacuole, and besides these 

 only the temporary organs known as ectoplasm, endo- 

 plasm, and pseudopodia. It has no tissues, unless we 



1 Supposed instances of conjugation in A. proteus have been described, 

 but it has not been shown that the gametes belonged to this species. 

 Conjugation is known in other kinds of Amceba. 



2 They are not ccenocytes, which are specialised parts of the proto- 

 plasm of the body, whereas Pelomyxa is a whole body. Groups of 

 similar, unseparated energids are known as syncytia. They may be 

 Plasmodia, formed by the union of free energids, or symplasts, formed 

 by the division of the nucleus of a single energid. A symplast may be 

 a cosnocyte, or the whole body of an organism. 



