THE MONERA. 77 



then undergoes fission into bodies, each of which passes direct- 

 ly into the form of the parent. 



In another genus (Myxastrum) an additional complication 

 is introduced ; the myxopod becomes encysted, and then di- 

 vides into many portions ; each of these elongates, and sur- 

 rounds itself with a delicate, fusiform, silicious case. Thus 

 inclosed, the germs are set free by the bursting of the cyst ; 

 and, after a while, the contents of the silicious cases emerge, 

 and pass at once into the myxopod state. 



In other genera, not only does the myxopod become en- 

 cysted before it undergoes fissive multiplication, but the forms 

 thus produced differ from the myxopod in being free-swim- 

 ming organisms, propelled by a long vibratile filament or fla- 

 gellum, like those flagellate Infusoria which are termed "mo- 

 nads." After swimming about for a while, these mastigopods 

 draw in their flagella, and become creeping myxopods. This 

 cycle of forms is exhibited by the genus Protomonas of 

 Haeckel. Lastly, in Protomyxa (Fig. 1) (Haeckel), there is 

 an alternation of a mastigopod (d) with a myxopod form (e), as 

 in Protomonas. But each myxopod does not usually become 

 encysted alone. On the contrary, a certain number of the 

 myxopods unite together, and become fused into an active 

 Plasmodium (/'), which exhibits no trace of their primitive 

 separation. The plasmodium becoming quiescent and sphe- 

 roidal, surrounds itself with a structureless cyst (a), divides 

 into numerous portions (&), w T hich are converted into flagellate 

 mastigopods, and these finally return to the myxopod condi- 

 tion (c, d, e). The cycle of life is here singularly similar to 

 that presented by the Myxomycetes, which have hitherto been 

 usually regarded as plants. 



There is no means of knowing whether the cycle of forms 

 presented bv Protomonas and Protomyxa is complete, or 

 whether some term of the series is still wanting ; and, con- 

 sidering how low down among plants the sexual process oc- 

 curs, it seems quite possible that some corresponding sexual 

 process yet waits to be discovered among the Monera. It is 

 posible that the fusion of separate Myxodictya and Proto- 

 myxm into a plasmodium may be a process of sexual conjuga- 

 tion. On the other hand, it may well be that these extremely 

 simple organisms have not yet reached the stage of sexual 

 differentiation. 



The Foramistifera. — Doubtless many Monera remain to 

 be discovered, but they will probably be minute and inconspic- 



