ORGANIZATION OF RHIZOPODA 



163 



the purpose of locomotion and ingestion of food, while a flagellum is present 

 as a permanent structure (Fig. 73). Such organisms, though usually placed 

 amongst the Rhizopoda, might with equal justification be classed with 

 the Mastigophora. 



The majority of the Rhizopoda possess a single nucleus, which divides 

 only when multiplication occurs. In some cases, however, two nuclei are 

 present, while in others the organisms are multinucleate. Some of the 

 multinucleate forms (Mycetozoa) are relatively large, each consisting of 

 a sheet of cytoplasm (plasmodium) easily visible to the naked eye. Re- 



\ 



m 



- o 



I. 



M 



'P 



m 9j 



m 



m^ 



Fig. 73. — Mastigina hylw : Free and Encysted Stages ( x 1, 

 (After Collin, 1913 



1. Free amoeboid form with four nuclei, to one of which a flagelkim is attached. 



2. Encysted form with two nuclei. 3. Encysted form with four nuclei. 



production amongst Rhizopoda usually takes place by binary fission, or 

 simple division into two more or less equal parts. In association with 

 encystment, when a protective capsule is formed around the organism, 

 the single nucleus, by repeated divisions, may give rise to a number of 

 nuclei, and the multinucleate cytoplasmic body within the cyst then 

 segments into a corresponding number of daughter individuals. The 

 latter may be amoeboid organisms, like the adults from which they were 

 derived, or they may be flagellated bodies which swim about for some 

 time before losing their flagella and again becoming amoebae. In the case 

 of some of the Foraminifera, there is a complicated life-cycle involving 



