364 Transactions of the Society. 



and Famintzin, in their classic work on Ceratiomyxa* (1) The 

 cnshion stage already described. From the cushions finger-like 

 processes grow in (2) the expansion stage. In these the plasmodium 

 forms at first a sponge-like network, but as they attain their full 

 lenoth the network concentrates on the surface and forms there an 

 enveloping layer; this is (o) the nctworl: stage. The network 

 divides up to form (4) a mosaic of cells, which completely covers 

 the upper part of the gelatinous sporophore, and is more loosely 

 distributed in the lower part ; this mosaic stage soon passes into 

 (5) the spore-hearing stage, when each cell pushes outwards and 

 grows into a long-stalked spore. It is at the beginning of the 

 network stage that Dr. Jahn discovered that all the nuclei of the 

 Plasmodium undergo a reduction division.f Preparations kindly lent 

 to me bv him show nuclei iu all stages of mitosis in rather stout 

 strands of protoplasm measuring 11-17 /it across (PL XI, fig. 6 a-d). 

 When a little later the network has become closer and its strands 

 more slender the daughter-nuclei have already separated. A 

 certain number of the latter stain very darkly and degenerate, and 

 are often to be seen in stainings of young spores lying beside the 

 perfect nucleus (PI. XI, fig. 6 /). It is probable that we see here 

 " a process of elimination " (to use Professor Minchin's words t) " of 

 effete or negative chromatin preceding the formation of the gametes 



♦ M. S. Woronin and A. S. Famintzin (1873) " Ueber zwei ueue Formen von 

 Schleimpilzen." M6m. de I'Acad. Imp. Petersbourg, ser. 7, xx. p. 4. 



t E. Jabn (1908), Myxomycetenstudieu. 7. Ceratiomyxa. Ber. Deutsch. Bot. 

 Ges., xxvi. d. p. 342. 



X Minchin (1912), " An Introduction to Protozoology," p. 142. 



EXPLANATION OF PLATE XI. 



Figs. 1-8. — Physamm didermoides (Ach.) Rost. 



,, 4-5. — Didymium squamulosum (A. & S.) Fries. 

 Fig. 7. — Ceratiomyxa fruticulosa 0\lMe\l.) M.diChv. 



Fig. 1. — Swarm-cell : a, with resting nucleus ; h, with dividing nucleus. 



,, 2. — A zygote or young Plasmodium, with a single nucleus undergoing mitotic 

 division, and a digestive vacuole which contains the remains of a 

 swarm-cell. 



,, 3. — Young Plasmodium, with two nuclei ; a shows a digestive vacuole con- 

 taining food. 



,, 4. — Ditto, with three nuclei ; a swarm-cell lies beside it. 



,, 5. — Ditto, with five nuclei. 



,, 6. — Strand of protoplasm from the network stage of the young sporophore, 

 showing in a, resting nuclei ; in h, c, nuclei dividing ; in d, e, 

 daughter-nuclei separated ; e is from a late network stage ; /, cells 

 from mosaic stage. In c, d, e, f, darkly-staining degenerate nuclei 

 are seen. 



,, 7. — a. Ripe spore, with four nuclei ; b to e, spore contents dividing ; /, group 

 of eight young swarm-cells just acquiring flagella ; g, h, swarm-cells, 

 with lengthening flageUa. 



All the figures on this plate are drawn from preparations made 

 by Dr. E. Jahn ; magnified 930 times. 



