THE SARCODINA 



239 



closed actually within the system of tubes. Nothing similar to the 

 1'nellae is known in any Foraminifera. 



For the classification of the Xenophyophora and their genera see 

 Schulze (290). 



IV. MYCETOZOA. 



The Mycetozoa are a group of semi-terrestrial Rhizopods occur- 

 ring in various situations, especially on dead wood or decaying 

 vegetable matter of various kinds. Their most characteristic 

 features are the formation of plasmodia, which represent the adult, 

 vegetative phase of the life-history, and their method of repro- 

 duction, consisting in the formation of resistant spores very similar 

 to those of fungi. The Mycetozoa were originally classified amongst 

 the Fungi as a group under the name Myxomycetes, but the in- 

 vestigations of de Bary first made clear their Rhizopod affinities. 



The life-history of a typical member of this group exhibits a 

 succession of phases, the description of which may conveniently 

 begin with the spore. Each spore is 

 a spherical cell with a single nucleus, 

 enclosed in a tough protective envelope 

 which enables it to resist desiccation. 

 It may be dormant for a considerable 

 period, and germinates when placed 

 in water. The envelope bursts, and 

 the contained cell creeps out as 

 an amoebula with a single nucleus 

 (Fig. 97), the so-called " myxamoeba." 

 After a tune the amcebula develops 

 a fiagellum, and becomes a flagellula 

 or zoospore (" myxoflagellate"), which 

 feeds and multiplies by fission. The 

 flagellula (Fig. 98) retains its amoeboid 

 form, and sometimes also the amoeboid method of locomotion, the 

 fiagellum appearing to act as a tactile organ. It captures bacteria 

 and other organisms by means of its pseudopodia, nourishing itself 

 in a holozoic, perhaps also in a saprophytic, manner. It also 

 may become temporarily encysted. 



The flagellate phase is succeeded by a second amoeboid stage, 

 the flagellum being lost. The amoebulae of this stage tend to con- 

 gregate together in certain spots, and the groups thus formed fuse 

 together (their nuclei, however, remaining separate) to form the 

 plasmodium, fche dominant vegetative stage, which feeds and grows, 

 its nuclei multiplying as it does so, until from the small mass of 

 protoplasm formed originally by the amoebulae, with relatively few 

 nuclei, it becomes a sheet or network of protoplasm, which may 



FIG. 97. The hatching of a spore 

 of Fvligo septica. a, Spore ; b, 

 c, contents emerging and under- 

 going amoeboid movements prior 

 to the assumption of the flagel- 

 lula-stage ; d, flagellula. c.v., 

 Contractile vacuole. After Lister, 

 magnified 1,100. 



