EDMONDSON — PROTOZOA OF IOWA. 45 



Family, ASTASIID^. 



ASTASIA Ehrenberg. 



Body elongate, plastic, changeable in form; flagellnm single, 

 arising from the anterior extremity; endoplasm transparent. 



Astasia trichophora Ehr. 



Body elongate, wider posteriorly, tapering toward the narrow 

 anterior extremity. Flagellnm long and thick. Nucleus cen- 

 trally located; contractile vesicle in the anterior region. 



Length of the extended body, 30-60 microns. (Figs. 72-7-^, 

 PI. X.) 



Astasia trichophora is interesting because it bears evident marks 

 of ancestral characters. The body of the organism is exceedingly 

 plastic, yet progress in development has gone so far as to render 

 the periphery a sufficient resistant to the endoplasm that no pseu- 

 dopodia are produced. The amoeboid changes of form are due to 

 contraction of the peripheral protoplasm, usually in a longitud- 

 inal direction. 



When freely moving Astasia is usually elongate with the nar- 

 row extremity in advance, then suddenly it doubles on itself or 

 contracts into an irregular mass, resuming the elongate form 

 again as it continues its course. 



At times the posterior border may be prolonged into a short 

 tail-like extension. At the base of the long, thick flagellum is 

 a more or less distinct oral opening which leads into a pharyn- 

 geal tube which is highly extensile. No eye-spot or coloring mat- 

 ter is developed, the endoplasm being transparent. 



Figure 72, Plate X, represents an elongate form. Fig. 73, PI. 

 X, a partially contracted individual. Astasia trichophora is found 

 almost everywhere in fresh water, commonly occurring among 

 diatoms, algse, etc. 



DISTIGMA Ehrenberg. 



Body changeable in form, more or less elongate when extended. 

 Flagella two in number, unequal in length, both directed for- 

 ward. Oral opening at the base of the flagella leading into a 

 long pharynx. Endoplasm transparent. 



DiSTIGMA PROTEUS Ehr. 



Body exceedingly plastic, when contracted greatly distended 



