454 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The wandering cells finally collect into sessile or stalked masses, 
or sori, and pass into an encysted state in which the masses are 
either naked aggregations or else are enclosed in a secreted mucous 
substance. After resting thus for some time, favorable conditions 
will again induce the rejuvenation of the cysts and the resumption 
of the vegetative stage. 
The Labyrinthuleae are thus distinguished from the Myxomycetes 
by the fact that the period of vegetation presents but a single 
phase which is comparable in a way to the plasmodial condition of 
the more highly differentiated group, for the reason that the vegeta¬ 
tive mass results from the contact or partial fusion of many individ¬ 
uals, each of which retains complete or only partial individuality. It 
is further apparent that the periods of fructification in the two 
groups are also comparable, although the somewhat indefinite aggre¬ 
gation through a general contraction or heaping up of the vegetative 
mass and the subsequent encystment in sessile or stalked masses of 
the one, are sufiiciently far removed from the well defined phenom¬ 
ena presented by the other. 
The third order to be considered, the Acrasieae, is represented 
by a small group of saprophytic organisms comprising seven genera 
and twenty species. Their spores or pseudospores, when they ger¬ 
minate, send forth myxamoebae which always remain in the amoe¬ 
boid state and which at no stage assume the peculiar flagellate or 
zoospore condition which characterizes the swarm cells of the Myxo¬ 
mycetes. The vegetative myxamoebae thus produced, absorb nutri¬ 
ment and become greatly increased in numbers by successive division. 
After a period of vegetation as separate and independent individ¬ 
uals, the amoeboid cells pass into a fructifying or resting condition. 
Through some contagious impulse, numerous myxamoebae move 
toward central points and become collected into definite colonies, or 
pseudoplasmodia,’’ sometimes called ‘^aggregation plasmodia.’’ 
The heaped up cells forming these colonies do not fuse, nor do they 
undergo any nuclear changes, but each member retains its individ¬ 
uality throughout further development, and becomes a spore or 
pseudospore, or else is used in the formation of a stalk which may 
eventually raise the sorus above the substratum. The resultant 
fructifications present many variations both in complexity and in 
general appearance. In the simpler species, the sessile or stalked 
sori recall to a certain extent the corresponding conditions which 
