334 PROCEEDINGS OF THE AMERICAN ACADEMY. 



here employed, since it expresses with sufficient exactness the actual 

 conditions. 



It will be noted further that in characterizing the Acrasieae as a 

 whole, emphasis has been laid on the fact, usually overlooked in accounts 

 of these organisms, that the vegetative stage ends before the pseudo- 

 plasmodium condition begins. The latter, therefore, is a phenomenon con- 

 nected not with vegetation but with fructification, and is by no means 

 homologous with the plasmodium of true Myxomycetes; nor is it com- 

 parable to the vegetative net-plasmodium of the Labyrinthuleae. 



I have followed Zopf, moreover, in characterizing as a " net-plasmo- 

 dium " the peculiar form of association occurring in the Labyrinthuleoe, 

 although it appears to be doubtful whether, in all cases at least, the con- 

 dition thus distinguished represents a true fusion, or whether the relation 

 is merely one of contact. 



SOROPHOREtE Zopf. 



Amcebas of the usual irregular myxamceba form or more or less reg- 

 ular and spindle-shaped, never possessing a swarm spore stage, forming 

 either a pseudoplasmodium or a net-plasmodium ; resting bodies borne 

 in sessile or stalked sori, which are either naked or imbedded in a 

 gelatinous matrix. 



ACRASIEiE Van Tieghem. 



Saprophytic, usually coprophilous, organisms, having two definitely 

 recurring stages, — a vegetative period, in which independent myxamoebaa 

 crawl about by means of amoeboid movements and undergo multiplication 

 by division ; and a fructifying period, in which the myxainccbse typically 

 aggregate into colonies called pseudoplasmodia and form either spores 

 or pseudospores, held together by a mucus substance, and borne in 

 stalked or sessile naked masses, or sori. 



SAPPINIACE^E. 



Myxamcebas comparatively large, with lobose pseudopodia. The 

 resting sta^e consisting either of a single encysted individual or of 

 many individuals encysted in masses at the ends of projections of the 

 substratum. 



This group is included here only provisionally, since the amoeba? 

 normally become encysted singly, thus forming microcysts, and do not 

 show the characteristic phenomenon of aggregation, or colony formation. 

 The aggregations which, it is true, often occur at the distal ends of 



