INTKODUCTION. 
Fries gave the name of Myxogastres, in 1833, to the group of 
organisms described in this Monograph, placing it among the 
Gasteromycetous Fungi. In 1836 Wallroth substituted the term 
Myxo7nycetes (Schleimpilze) for the older name, and this came to 
be the generally accepted designation. Later investigations showed 
that the spores, instead of producing a mycelium, as in the case of 
fungi, gave bii'th to sioarm-cells, which coalesce to form a Plasmo- 
dium. In consequence of this discovery, which indicated a relation- 
ship with the lower forms of animal life, de Bary in 1858 introduced 
the name Mycetozoa. Under this head he still retained the term 
Myxomycetes for the section so named by Wallroth, but linked with 
them the Acrasiece of Van Tieghem, a small group inhabiting the 
excrement of animals ; in these the spores are said to produce 
swarm-cells, as in the Myxomycetes, which multiply by division 
but do not coalesce to form a plasmodium. At a certain period, 
when the fruits are about to be formed, they become attached 
in branching strings which concentrate to a point, where they 
are massed together in aggregations of more or less definite 
shape ; the swarm-cells, however, do not lose their individuality. 
In Dictyostelium, a genus of the Acrasiece, a stalk is formed by 
the arrangement of a number of swarm-cells in vertical rows in 
the centre of the heap ; the surrounding amoeboid bodies creep 
up this stalk and form a globose cluster at the extremity ; here 
each amoeboid swarm-cell acquires a spore-wall, and they become 
a naked aggregation of spores not enclosed by a definite sporangium- 
wall. Eostafinski followed de Bary in the view that the formation 
of a Plasmodium indicates a wide separation in the natiu'al 
position of the Myxomycetes from the fungi, but he suppressed 
that name entirely, adopting de Bary's class name Mycetozoa in 
its place; at the same time, he admitted into his Monograph 
Dictyostelium, a genus of the Acrasieoi. The reason for his including 
this genus may be the fact pointed out by de Bary, that Brefeld 
in first describing the dense aggregations of swarm-cells into the 
stalked spore-masses of Dictyostelium,, refers to them as being 
" pla,smodia ; that is, products of the coalescence of swarm- 
cells ; " and it was not until after the pul)]ication of Rostafinski's 
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