472 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
and stained with various reagents but no nuclear changes have been 
observed in the individuals, nor have any indications of increase in 
numbers by division of the myxamoebae been seen, from the first 
period of aggregation up to the maturation of the fructification. In 
this respect, the pseudoplasmodium is totally unlike the comparable 
•^aggregated’’ plasmodium of the Myxomycetes, in which nuclear 
division precedes the formation of spores. During any stage of its 
development, the pseudoplasmodium may be satisfactorily stained 
and permanently mounted after the fixing agent has sufficiently 
coagulated the mucus which encloses the individuals and causes the 
mass to cohere, so that division, if it were present, could be very 
readily demonstrated. 
The Fructifying Stage. 
As has been stated above, the ultimate purpose of the formation 
of colonies of individuals is the production of naked masses of rest¬ 
ing bodies, either spores or pseudospores, which are formed in fructi¬ 
fications having varied appearance and habit. These colonies, or 
pseudoplasmodia, develop therefore into fructifications which show 
increasing complexity of structure, from the slightly differentiated 
sessile aggregations of the simpler species of the Guttidmaceae to 
the complex stalked sori of the Dictyosteliaceae. The fructifications 
of the simpler forms are in fact little more than heaped up masses 
of encysted individuals, while those of the higher forms, on the other 
hand, possess characters which, in their parenchyma-like stalk cells 
having walls of cellulose, present a degree of differentiation even 
surpassing in some respects that seen in the fructifications of the 
allied Myxomycetes. 
In all the members of the group, with one exception, the sorus of 
resting individuals, which is borne either sessile on the surface of the 
substratum or at the end of a stalk of varying length and structure, 
forms a globular or somewhat irregular mass. In the single genus 
Acrasis, however, the conditions are exceptional, in that, according 
to van Tieghem, a single row or chain of spores surmounts a slender 
supporting filament which is likewise made up of a single row of 
superposed cells of varying number. 
It is convenient in the following account of the fructifying period 
