908 THE ANIMAL KINGDOM. 



CLASS MYCETOZOA. 



Rhizopod Protozoa (?) with coated spores s. chlamydospores, giving origin 

 to amoebulae, which may or may not become temporarily zoospores or 

 flagellulae. The amoebulae grow and multiply by binary fission ; they then 

 either collect together into a mass or aggregation-plasmodium, every Amoeba 

 in which is converted into a chlamydospore ; or they fuse together and form 

 a multinucleate fusion-plasmodium^ which continues to grow, but eventually 

 encysts and is converted into chlamy do spores. Inhabiting moist and decaying 

 wood, vegetable debris or dimg. 



The spore of a Mycetozoan is a minute spherical or oval body, 

 becoming concavo-convex if dried, inclosed in a membrane or episporium. 

 This membrane may be smooth or ornamented in various ways, generally 

 colourless, violet or violet-brown in the Calcariaceae, yellow or red in 

 Trichiaceae, &c. The contained protoplasm is dense and variably granular ; 

 it lodges a single nucleus, or two if the spore is of unusual size. When 

 the spore is suitably moistened and begins to germinate, two contractile 

 vacuoles make their appearance, and the episporium bursts as the proto- 

 plasm swells. As soon as the latter is set free, it undergoes in Ceratium 

 (i. e. Exosporea) binary fission repeated three times, the products of fission 

 remaining together until the process is complete. But as a rule it com- 

 mences life as an amoebula, which moves actively about and secretes a 

 pellucid coat. Except in the Sorophora this amoebula developes a cilium 

 and assumes a temporary zoospore condition, and alternate phases, amoe- 

 boid and flagellate, may recur. The amoebula or Myxamoeba multiplies 

 by binary fission, but when it does so it becomes spherical and loses its 

 contractile vacuoles. If food is wanting, or other conditions of life un- 

 favourable, e.g. a lack of moisture, the Myxamoeba contracts into a sphere 

 and developes a more or less firm membrane. This resting phase is known 

 as the microcyst. When the conditions of life again become favourable, 

 the encysted protoplasm perforates the membrane at some one spot and 

 creeps out. 



After a period of growth the Myxamoebae begin to gather together, 

 and they either retain their individuality or fuse. The first of these two 

 alternatives obtains in the Sorophora. The collected Myxamoebae con- 

 stitute an aggregation- or pseudo-plasmodium. The heap they form 

 assumes a determinate shape and is known as a sorus. The Amoebae 

 which make it up either collect by degrees, and are transformed as they 

 collect into chlamydospores, as in Copromyxa, or they collect quickly. 

 Certain of them are then disposed in one or more linear series, enlarge, 

 become vacuolate, acquire a cellulose membrane, and form a stalk or 

 peduncle upon which the remaining cells are grouped. These cells are 

 each converted into a chlamydospore. 



