INTRODUCTION 11 



with the phenomenon of fructification, and cannot be regarded as 

 homologous with either the true Plasmodium of the Myxomycetes 

 or the net-plasmodium of the LabyrinthuUae. 



For details of the taxonomy of the group the student is referred 

 to the papers of Olive (1901: 1902). The families and genera 

 recognized by him as comprising the group are as follows: 



Acrasieae van Tieghem, 1880. 

 Sappiniaceae 



Sappinia Dangeard, 1896. 

 Guttulinaceae 



Guttulinopsis Olive, 1901. 



GuUulina Cienkovvski, 1873. 

 Dictyosteliaceae 



Acrasis van Tieghem, 1880. 



Dictyostelium Brefeld, 1869. 



Polysphondylium Brefeld, 1884. 



Coenonia van Tieghem, 1884. 



The group as treated by Olive contains about twenty species. 

 Prior to the appearance of his papers only one species had been 

 reported for North America. He grew a number of forms in pure 

 culture on solid media and in nutrient decoctions. He also 

 studied stained preparations, and figures nuclei. No indication 

 of nuclear fusion was observed. If sexuaHty exists in the group 

 it is as yet undiscovered. 



Labyrinthuleae. — This group, founded by Cienkowski (1867), 

 is composed of a small number of very primitive and imperfectly 

 known organisms characterized by the presence in the vegetative 

 phase of a peculiar structure termed a net-plasmodium. This 

 was thought by Zopf (1892) to constitute a vegetative condition 

 intermediate in character between the aggregation-plasmodium 

 of the Acrasieae and the true Plasmodium of the Myxomycetes. 

 He erected the group Sorophoreae to include the Acrasieae and 

 Labyrinthuleae. As now understood the Labyrinthuleae embrace 

 two genera, Lahyrinthula Cienkowski (1867) with three species 

 parasitic on algae, and Diplophrys Barker (1868) with one 

 coprophilous species and another doubtful form said to be 

 aquatic. 



In the beginning of the vegetative phase the Labyrinthuleae 

 exist as motile fusiform (spindle-shaped) cells, each of which 

 is provided with two radiating tufts of delicate pseudopodia 

 situated at the opposite poles. These cells may remain separate, 

 but when they come in contact their pseudopodia usually fuse. 



