THE SARCODINA 



239 



ctf 



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

 linellse 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 amcebula with a single nucleus 



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



After a time the amcebula develops 



a flagellum, and becomes a flagellula 



or zoospore (" myxo flagellate"), which 



feeds and multiplies by fission. The 



flagellula (Fig. 98) retains its amceboid 



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



flagellum 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 anicebulse 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, the 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 ainoebulee, with relatively few 

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



FIQ. 97. The hatching of a spore 

 of Fuligo septica. a, Spore ; b, 

 c, contents emerging and under- 

 going am oaboid movements prior 

 to the assumption of the nagel- 

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

 Contractile vacuole. After Lister, 

 magnified 1,100. 



