THE SIMPLEST FORMS OF LIFE 33 



and needing moisture for its growth. If threatened 

 with drying up it may contract and secrete a protec- 

 tive covering about itself. 



The reproduction is purely non-sexual, and consists 

 in the breaking up of the protoplasm into a great many 

 parts, as in the Monera ; but in the slime-moulds the 

 cells thus formed secrete a definite protective covering 

 or cell- wall, and closely resemble the spores or repro- 

 ductive cells of the Fungi, with which these organisms 

 are often classed ; but the general opinion at present 

 is that they are forms allied to the Monera, which have 

 not yet become sufficiently differentiated to show defi- 

 nite animal or plant characters. 



The most specialized forms among the slime-moulds, 

 like the ones figured (Fig. 4), show a curious resem- 

 blance to true plants in their reproductive parts, 

 although these resemblances are purely superficial. 

 Thus they form spore-cases or " sporangia " of definite 

 and characteristic shapes (B), within which the proto- 

 plasm divides into a great many nucleated fragments, 

 as in the Monera ; but here, as we have seen, each por- 

 tion secretes a definite cell-membrane and forms a 

 spore, much like an ordinary plant-cell (Fig. 4, C), 

 and capable of being dried up without losing its vital- 

 ity. With these spores are found in the higher forms 

 curious thread-like structures of various kinds. 



The spores, on being placed in water, soon burst open 

 and set free the contained protoplasm, which assumes 

 the form of a free-swimming, naked cell or swarm- 

 spore, like that of the Monera, and resembling closely 

 certain low animal forms, the flagellate infusorians 

 (Fig. 4, D). In this condition the slime-mould con- 



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"UNIVERSITY 



