452 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
for study, besides several forms which have appeared in laboratory 
cultures in Cambridge. To Professor Farlow, also, I am under great 
obligations, and to Miss Josephine Clark of the Library of the 
Department of Agriculture, I am indebted for the Russian publica¬ 
tion of Cienkowsky on Guttulina. 
Introduction. 
The Acrasieae comprise a small group of organisms, which have 
been associated by van Tieghem and de Bary wdth the Myxomyce- 
tes. Although these two orders present but slight resemblances in 
their fructifying conditions, they agree in the possession of an 
amoeboid state and also in the formation of naked protoplasmic 
masses during certain periods of their life history. Zopf in recent 
years (’92) associated also the Labyrinthuleae with the two above 
mentioned orders, since he thought that in their formation of the 
so called “ net-plasmodium,’’ they presented a vegetative condition 
which might be regarded as intermediate between the aggregation- 
or pseudo-plasmodium of the Acrasieae and the true plasmodium of 
the Myxomycetes. A brief summary of the salient characters of 
these three groups will serve to recall the main features of their 
developmental history. 
The spores of the Myxomycetes, on germinating, produce swarm 
cells which swim about in the water with a peculiar dancing motion, 
each bearing at its forward end a flagellum by which it is propelled. 
After swarming thus for some time, the flagellum is retracted and 
the cells assume a myxamoeba condition, during which they crawl 
about by means of amoeboid movements. During either of these 
stages, slow drying or similar unfavorable conditions may induce 
the temporary encystment of the individuals, which thus form 
isolated microcysts,” and which may be revived into the active 
state on the addition of water. Following the normal development, 
however, the amoeboid individuals, after greatly multiplying by 
successive division, ultimately become aggregated and coalesce to 
form a mass of naked protoplasm. This vegetative mass, called the 
plasmodium, may likewise become multiplied by fragmentation as 
well as through the formation, under certain adverse conditions, of 
“sclerotia,” compacted masses of small cysts, each capable of renew- 
