326 THE MICROSCOPE AND ITS REVELATIONS. 



upon decayed wood, bark, heaps of decaying leaves, tan-beds, etc. ; 

 spreading over damp surfaces as a plasmodium, or network of naked 

 protoplasmic filaments (Fig. 208, A), of a soft creamy consistence, and 

 usually of a yellowish color. The filaments of this network exhibit 

 active undulatory movements, which in the larger ones are visible under 

 an ordinary lens, or even to the naked eye, but which it requires micro- 

 scopic power to discern in the smaller. With sufficiently high amplifica- 

 tion, a constant movement of granules may be seen flowing along the 

 threads, and streaming from branch to branch. Here and there off- 

 shoots of the protoplasm are projected, and again withdrawn, in the 

 manner of the pseudopodia of an Amoeba; while the whole organism may 

 be occasionally seen to abandon the support over which it had grown, 

 and to creep over neighboring surfaces, thus far resembling in all 

 respects a collosal ramified amoeba. It is also curiously sensitive to light, 

 and may sometimes be found to have retreated during the day to the 

 dark side of the leaves or into the recesses of the tan over which it had 

 been growing, and again to creep out on the approach of night. After a 

 time there arise from the surface of this plasmodium oval capsules or 

 sporangia (B, a, a', b), within which the reproductive bodies or 'spores' 

 are developed, and which burst when mature to give them exit. Each 

 'spore' is a spherical cell (c) inclosed in a delicate membranous wall; 

 and when it falls into water this wall undergoes rupture (D) and an 

 Amo3ba-like body (E) escapes from it, consisting of a little mass of pro- 

 toplasm, with a round central nucleus inclosing a nucleolus, and a con- 

 tractile vesicle. This soon elongates (F), and becomes pointed at one 

 end, whence a lougflageHum is put forth, the lashing action of which 

 gives motion to the body. After a time, the flagellum disappears, and 

 the active movements of the spore cease; but it now begins to put forth 

 and to withdraw finger-like pseudopodia, by means of which it creeps 

 about like an Amoeba, and feeds, like that Rhizopod, upon solid particles 

 which it engulfs within its soft protoplasm. A ' conjugation ' then 

 takes place between two of these Myxammbm (H), their substance under- 

 going a complete fusion into one body (i), from which extensions are put 

 forth (K), that constitute the beginning of a new plasmodium. This 

 continues to grow by the ingestion and assimilation of the solid nutri- 

 ment which it takes into its substance; and, by the ramification and 

 inosculations of these extensions, a network is formed resembling that 

 from which it originated, to bear sporangia in its turn, from which a 

 new cycle will commence. 



323. Under certain conditions not yet perfectly understood, the 

 Myxomycetes have been observed to pass from the active into the ( rest- 

 ing ' state; and this may occur both in the amoeboid spores and in the 

 plasmodium. The former return to the spherical form, and surround 

 themselves with a firm envelope; and in this 'encysted' condition they 

 may be dried-up so as to be carried about as dust, resuming their origi- 

 nal activity when again placed in water. When the plasmodium is 

 about to pass into the 'resting' state, it withdraws its finer branches, 

 and expels such solid ingesta as may be included in it; and its motions 

 then gradually cease, It then either breaks up into a multitude of poly- 

 hedral cells (?), which, however, remain connected in one body, that 

 dries into a horny brittle mass termed 'sclerotium;' or separates into a 

 number of fragments of unequal size, which take a spherical form and 

 become ' encysted ' in a double envelope. Both these ' resting ' forms 

 may undergo desiccation without the loss of their vitality. When, after 



