222 



THE PROTOZOA 



uninucleate amoeba, which reproduces itself by binary fission of the 

 ordinary type ; but large multinucleate forms occur which become 

 encysted. Within the cyst the nuclei break up into chromidia, 

 from which a great number of secondary nuclei are formed. The 

 protoplasm becomes concentrated round the secondary nuclei to 

 form a number of small cells, which acquire flagella and are set free 

 from the cyst as flagellulse, believed to be gametes and to copulate ; 

 the zygote is at first encysted, but becomes free from the cyst, and 

 develops into the uninucleate amoeba. The life-cycle of A. proteus 

 is possibly of this type, since in this species also multinucleate 

 amoebae are commonly observed (see especially Stole ; compare also 

 Paramceba (Fig. 49). 



Fia. 88. Amaha diploidea. A, The amoeba in the vegetative condition, with 

 its two nuclei ; B F, the sexual processes within the cyst, drawn in outline 

 on a reduced scale ; B, two amoebae, each with its two nuclei, encysted together, 

 the nuclei beginning to give off chromidia ; C, the two nuclei of each amoeba 

 fused, numerous vegetative chromidia in the cytoplasm ; D, the bodies of 

 the amoebae fused, each synkaryon beginning its reduction-process ; E, the 

 synkarya giving off reduction -nuclei which are degenerating ; F, the reduction- 

 process complete ; the cyst contains a single amoeba with two nuclei (syn- 

 karya), ready to emerge and begin its vegetative free life. After Nagler (95). 



Metcalf (257) describes " gemmules " budded from small free amoebae of 

 the proteus-type, each gemmule becoming detached and developing into a 

 flagellated gamete of a cercomonad type. The flagellulse were observed 

 frequently to lose their flagella and become amoeboid. Copulation of two 

 flagellulae took place to form an amoeboid zygote. Metcalf's observations 

 upon the syngamy in this case recall strongly the observations of Jahn (294) 

 on the sexual processes of Mycetozoa (p. 242). It is possible that the syngamy 

 observed by him did not form a part of the life-cycle of the amoeba, but of 

 some other organism. 



The sexual process described by Nagler (95) in Amoeba diploidea is of a 

 remarkable kind (Fig. 88). In the ordinary vegetative condition the amoeba 

 possesses normally two nuclei, which divide simultaneously each time the 



