SARCODINA, PROTEOMYXA 177 



meters. Colonial Sarcodina, especially plasmodium-forming 

 Mycetozoa, reach a considerable size. 



Asexual reproduction is usually by binary (or rarely by mul- 

 tiple) fission, budding, or plasmotomy. Definite proof of sexual 

 reproduction has been given in a comparatively small number. 

 Encystment is common in the majority of both free-living and 

 parasitic Sarcodina, but it is unknown in certain groups. The 

 life-cycle has been worked out in a few forms. It seems to vary 

 in different groups. The youngest stages are either amoeboid or 

 flagellate, and on this account it is sometimes very difficult to 

 distinguish the Sarcodina and the Mastigophora. In some forms 

 the adult trophic stage may show an amoeboid or flagellate 

 phase owing to differences in environmental conditions (p. 205). 

 These points support strongly the view that both classes have 

 descended from a common ancestor and have undergone evolu- 

 tionary changes in two different directions. 



The Sarcodina are divided into two subclasses, as follows : 



With lobopodia, myxopodia, or filopodia Subclass 1 Rhizopoda 



With axopodia (usually radiating) Subclass 2 Actinopoda 



SUBCLASS 1 RHIZOPODA SIEBOLD 



The term Rhizopoda is often used to designate the class but 

 is used here for one of the subclasses. These Sarcodina possess 

 pseudopodia which are not axopodia. The subclass is divided 

 into five orders as follows: 



Without test 



With radiating pseudopodia Order 1 Proteomyxa 



With rhizopodia; forming plasmodium Order 2 Mycetozoa 



With lobopodia Order 3 Amoebaea 



With test 



Test single-chambered; chitinous Order 4 Testacea 



Test one to many chambers; calcareous Order 5 Foraminifera 



ORDER 1 PROTEOMYXA LANKESTER 



A number of incompletely known Rhizopoda are placed in 

 this group. They possess few common characteristics. The 

 pseudopodia are filopodia which often branch or anastomose 

 with one another. In this respect the Proteomyxa show affinity 



