PL A SMODROMA TA 



299 



Ectoplasm only seen in outbursts. Nucleus with 

 finely divided chromatin forming a membrane-like 

 contour and with definite karyosome. Division 

 by promitosis — -Vahlkamfia. 



II. Typically binucleate, the two nuclei having the same 

 size and structure. 

 Ecto- and endoplasm distinct — Dientamoeha. 



B. With uniflagellate stage : — ■ 



Ectoplasm visible on movement. Endoplasm with or 

 without a body like a Nehenkorper — Craigia. 



THE GENUS AMGEBA. 



The old original genus Amoeba seems to have been first described 

 by Rosel von Rosenhof in 1775, under the heading the Small 

 Proteus, and to this organism Linnaeus gave the name Volvox chaos, 

 which Pallas in 1766 turned into Volvox proteus. In 1822 Baron 

 Bory de Saint Vincent, in the ' Dictionnaire Classique d'Histoire 

 Naturelle,' vol. i., pp. 260-262, established the genus Amiba, calling 

 Volvox proteus by the name Amiba divergens, which Ehrenberg in 

 1 831 altered to Amceha princeps and Leidy in 1878 to Amoeba 

 proteus. 



This original genus is now divided into the following genera : — 

 A. Usually free living : — ■ 



I. Without a flagellate stage in the life-cycle: — 

 (a) Usually uninucleate. 



1. Large forms reaching to i millimetre in diameter, 



free living, with well differentiated ecto- and 

 endoplasm and well developed pseudopodia. 

 One or many large nuclei with doubly refracting 

 membrane and chromatin concentrated into a 

 single large karyosome or as granules diffused 

 through nucleus. One or more contractile 

 vacuoles — Genus i. Amoeba Bory de St. Vincent, 

 1822. 



2. Minute forms, free living or commensal, ectoplasm 



not well differentiated from endoplasm, moving 

 as a fingei -formed single pseudopodium or with 

 irregular ectoplasmic bursts to form a general or 

 local ectoplasm. Nucleus single or double, with 

 finely divided chromatin, forming a membrane- 

 like structure and a definite karyosome. One 

 contractile vacuole present as a rule — Genus 2, 

 V ahlkamfia ChdXion and Lalung-Bonnaire, 1911; 

 emendavit Calkins, 1912. 

 [h) Usually binucleate. Genus 3, Dientamoeba Jeffs 

 and Dobell, 1918. 



