AMOEBOID PROTOZOA (SARCODINA) 211 



Previously unknown on account of their diminutive size, these 

 organisms at once attracted the early workers with the microscope. 

 Although Leeuwenhoek as early as 1675 initiated the study of 

 Protozoa by his discovery of Vorticella, an infusorian, without 

 doubt, Rosel's description of Amoeba proteus under the name " Der 

 kleine Proteus," in 1755, represents the first recorded observa- 

 tion of a fresh- water protozoon of the group Sarcodina. 



In 1835 Dujardin called the viscid, transparent substance com- 

 posing the bodies of marine Protozoa, which he then had under 

 observation, sarcode, but it was not until 1883 that Biitschli first 

 employed the term Sarcodina and included under it all forms of 

 Protozoa which move by means of protrusions of protoplasm from 

 the body proper, called pseudopodia. 



Most of the Sarcodina are very minute in size. Very few of 

 them can be seen by the unaided eye and none can be studied 

 with any degree of satisfaction without the aid of a compound 

 microscope. These forms vary greatly in general appearance. 

 Many of them are naked masses of protoplasm tending to be 

 globular when first placed under the microscope but soon assum- 

 ing variable shapes, protruding from the body, with more or less 

 rapidity, blunt, lobe-like, or filiform pseudopodia, often branching 

 and sometimes anastomosing. Others are provided with envelopes 

 or shells, very diverse in form and composition, sometimes secreted 

 by the animal itself, sometimes consisting of picked-up fragments 

 firmly cemented together. These envelopes may be compact and 

 rigid, or flexible, and are provided with one or more apertures 

 through which the pseudopodia are extended. Still other forms, 

 commonly known as the Heliozoa or "sun animalcules," are typi- 

 cally spherical, sometimes with shells of delicate structure and 

 always with fine ray-like pseudopodia, usually rendered somewhat 

 rigid by the presence of stiffened axial filaments. 



Fresh-water Sarcodina may be found in very diverse habitats 

 and within wide ranges of temperature. They occur from the 

 level of the sea to the tops of very high mountains. Perhaps no 

 other animals have such a vast altitudinal range as certain com- 

 mon species of Sarcodina. Roadside pools and also ponds, lakes 

 and rivers are habitats of myriads of these low organisms. In 



