THE MYCETOZOA 65 



SUB-CLASS II. SOROPHORA. 



A flagellate stage is absent from the life -history. The amoebulae 

 become aggregated prior to spore-formation, but do not fuse to form a true 

 plasmodium. In the more highly developed genera some of the aggregated 

 amoebulae are modified to form a stalk on which the remainder are borne 

 after encystment in naked clusters (sori). 



ORDER 1. Guttulinaceae. 



The aggregation of amoebulae, prior to spore-formation, to form the 

 pseudo-plasmodium, is incomplete in Copromyxa. The amoebulae have 

 the Umax form, and the shape of the sori is indefinite. 



Genera Copromyxa, Zopf (Fig. 19, a and 6). Sori wart-like or 

 spindle-shaped, 1-3 mm. high, formed on the surface of the nidus. None 

 of the amoebulae are differentiated to form a stalk. On horse and cow 

 dung. Guttulina, Cienk. Some of the aggregated amoebulae are dif- 

 ferentiated to form a short stalk on which the sorus is borne. On decaying 

 wood or horse-dung. 



ORDER 2. Dictyosteliaceae. 



A pseudo-plasmodium is formed prior to spore-formation. Some of 

 the aggregated amoebulae are modified to form a stalk. The sori have a 

 definite shape. Amoebulae with short pointed pseudopodia. Genera 

 Didyostelium, Brefeld. Stalks unbranched, the spores without definite 

 arrangement in the sori. On dung of herbivorous animals. A cram, van 

 Tieghem. Spores arranged in rows, like strings of beads, at the ends of 

 the stalks. On beer-yeast. Polysphondylium, Brefeld (Fig. 19, c and d). 

 Sori globular, on branched stalks, which attain 1 cm. in length. On 

 horse-dung. 



POSTSCRIPT. 



Since the foregoing account of the Mycetozoa was written papers .have 

 been published, in part of a preliminary character, which appear to throw 

 light on the nuclear history. 



In the Endosporeae, Fraulein H. Kriinzlin l has described a fusion of 

 the nuclei in pairs, prior to the mitosis which precedes spore-formation, in 

 the young sporangia of Arcyria, and this result is corroborated by Jahn. 2 

 The number of chromosomes at this division Jahn believes to be sixteen 

 (" 8 double chromosomes ") in Arcyria (at least double that which Jahn 

 found in the division of the zoospore in other genera). In Fuligo Harper 3 

 found the number to be twelve in the mitosis preceding spore-formation. 



1 " Zur Entwicklungsgescluchte der Sporangien bei den Trichien und Arcyrien," 

 Arch.f. Protistenkunde, Bd. ix. (1907), p. 170. 



2 " Myxomycetenstudien 6. Kernverschmelzungen und Reduktionsteilungen," 

 Eer. d. deutsch. botan. Gese.llschaft, Bd. xxv. (1907), p. 23. 



3 "Cell and Nuclear Division in Fuligo varians," Botanical Gazette, vol. xxx. 

 (1900), p. 217. 



