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 limax 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. Acra&is, van 

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

 the stalks. On beer- yeast. Polyspliondylium, 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 & ' 

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



1 "Zur Entwicklungsgesehichte der Sporangien bei den Trichieu und Arcyrien," 

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



2 " Myxomycetenstmlien 6: Kernverschmelzungen und Reduktionsteilungen," 

 Her. d. deutsch. botan. Gesellschoft, Bu. xxv. (1907), p. 23. 



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

 (1900), p. 217. 



