458 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
he proposes to include the Acrasieae and the Labyrinthuleae as 
coordinate orders under the name Sorophoreae. 
Brefeld (’84) was the next to discover another new form, which 
was evidently closely allied to Dictyostelium, and to which he gave 
the name Polysphondylium, and in this paper he described in great 
detail the developmental history of both related organisms. 
An amoeboid form, Sappinia, which is evidently similar to certain 
stalked amoebae mentioned by Cienkowsky in his paper on Giittu- 
Una rosea^ has been recently described by Dangeard (’96) and is 
included by him in the Acrasieae. In view, however, of the fact 
that the amoebae become encysted singly, and that, as will be noted 
hereafter, their aggregation when it occurs is probably accidental, 
they should perhaps be excluded from the present group, or are at 
least only to be admitted as doubtful members of it, although they 
may serve to suggest its possible beginnings. 
Finally, the writer, in a preliminary enumeration of the Soro¬ 
phoreae (:01), has followed Zopf in associating the Acrasieae and 
the Labyrinthuleae, and in that article has described several new 
species of the Acrasieae. 
In the following account of the Acrasieae, the development of the 
organisms composing the group has first been traced in some detail 
through both the vegetative and the fructifying stages; this is fol¬ 
lowed by the systematic arrangement of the species. Four genera 
only have been studied by the writer, namely, Sappinia, Guttulin- 
opsis, Dictyostelium, and Polysphondylium, while the original 
descriptions of the other three genera have been depended upon to 
supply data in the following comparative account. 
The Vegetative Stage. 
The life cycle of the Acrasieae is clearly separable into two well 
marked periods,— one of vegetation and one of fructification; the 
fructifying period may be still further divided into two secondary 
periods — a preliminary stage of colony formation, and another 
which embraces the formation and maturation of the resting bodies. 
During the vegetative stage, the myxamoebae live as separate and 
independent individuals, while during the subsequent fructifying 
