PROTOZOA I RHIZOPODA. 53 



CHAPTER II. 

 RHIZOPODA. 



GENERAL CHARACTERS OF THE RHIZOPODA. the Rhizopoda 

 may be defined as Protozoa which are destitute of a mouth, are 

 simple or compound, and possess the power of emitting "pseudo- 

 podia" They are mostly small, but some of the composite 

 forms, such as the sponges, may attain a very considerable 

 size. Structurally, a typical Rhizopod as an Amoeba is 

 composed of almost structureless sarcode, without any organs 

 appropriated to the function of digestion, and possessing the 

 power of throwing out processes of its substance so as to con- 

 stitute adventitious limbs. These are termed " pseudopodia," 

 or false feet, and are usually protrusible at will from different 

 parts of the body, into the substance of which they again 

 melt when they are retracted. They are merely filaments of 

 sarcode, sometimes very delicate and of considerable length, 

 at other times more like finger-shaped processes; and they 

 are somewhat analogous to the little processes which can be 

 thrown out by the white corpuscles of the blood and by pus- 

 cells. Indeed, it has been remarked by Huxley that an Amoeba 

 is structurally " a mere colourless blood-corpuscle, leading an 

 independent life." 



The class Rhizopoda is divided into five orders viz., the 

 Monera, the Amcebea, the Foraminifera, the Radiolaria, and 

 the Spongida, of which the last is occasionally considered as a 

 separate class. 



ORDER I. MONERA. This name has been proposed by 

 Haeckel for certain singular organisms which may provisionally 

 be regarded as the lowest group of the Rhizopoda. They are 

 very minute in size, and are distinguished by the fact that 

 the body is composed of structureless sarcode, capable of emit- 

 ting thread-like prolongations or pseudopodia, but destitute of 

 either nucleus or contractile vesicle. The pseudopodia are in 

 the form of delicate filamentous processes of sarcode, which 

 interlace and anastomose with one another in every direction, 

 and which exhibit a circulation of minute molecules and gran- 

 ules in their interior, and along their edges. The body, when 

 at rest, is more or less nearly circular in form, but it is capable 

 of undergoing manifold changes of figure. No hard covering 

 or " test " is ever developed. Reproduction is mostly by fis- 

 sion, with or without precedent encystation and quiescence. 



