32 DAVKNPORT ACADEMY OF SClENCE.S. 



sometimes branched. A single flagellum arising from the ante- 

 rior extremity. 



Mastigamceba sp. 



Body elongated, wider posteriorly. Pseudopodia extending 

 from all points of the surface, short, finger-like, unbranched. 

 Flagellum longer than the body, with a broad base. Nucleus 

 spherical; contractile vesicle single. 



Length, 15-25 microns. (Fig. 43, PI. VII.) 



A minute form corresponding to the above description has been 

 observed in pond water from several localities in this state. In 

 some respects the organism conforms to Mastigamceba siviplex S- 

 K., although the Iowa variety is usually wider posteriorly and 

 the pseudopodia are smooth. 



This species, as others of the genus, may be considered as 

 occupying an intermediate position between the Sarcodina and 

 Alastigophora, possessing as it does some striking characters of the 

 former. There is, however, not such a marked differentiation 

 between the endoplasm and ectoplasm as in Aniceba, which it 

 resembles, the outer surface also offering greater resistance to the 

 endoplasm than in Amceba. 



The flagellum shows indications of being an intermediate 

 structure, it apparently being but a prolongation of the anterior 

 extremity of the body with a broad base as if a tapering pseudo- 

 podium were long drawn out and endowed with the power of 

 vibration. 



No indications of a mouth are present, the food probably being 

 ingested at any point in the surface as in Amceba. 



Habitat, pond water among diatoms and other unicellular 

 plants. Found in Van Buren, I^ouisa and Johnson counties. 



ACINETACTIS Stokes. 



Spheroidal in shape, capable of extending capitate pseudopodia 

 from all points of the periphery. Flagella two in number, approx- 

 imately equal in length. 



AciNETACTis MIRABII.IS Stokes. 



Body nearly spherical, with slender capitate pseudopodia 

 extending from all parts of the periphery, these pseudopodia also 

 bear one or more protoplasmic swellings along the course of the 



