CHAPTER II. 



OF THE RHIZOPODA GENERALLY; THEIR ORGANIZATION AND PHYSIOLOGICAL 

 HISTORY; AND THEIR DISTRIBUTION INTO SUBORDINATE GROUPS. 



1 . Neither the Morphological characters nor the Physiological history of the Foraviinifera, 

 nor their position in the Animal Kingdom, can be properly understood, without a preliminary 

 survey of the entire Class of Rhizopoda (of which they constitute by far the most important 

 section), and an exposition of its most distinctive features as made known by modern 

 research. 



2. The Class of Rhizopoda constitutes, with the Classes of Porifera {Sponges), Infu- 

 soria, and Gregarinida (to all which it is very intimately related), the Sub-Kingdom which 

 Zoologists have now agreed to designate by the title PROTOZOA, indicative of the simplicity 

 of its type of organization, or, as it might be almost said, its deficiency in any definite organi- 

 zation. In none of its members can any traces be found either of a nervous or of a muscular 

 system; their digestive apparatus is reduced to its simplest possible condition; of a circulating 

 system a mere rudiment only can be distinguished ; special organs for respiration and excre- 

 tion seem altogether wanting ; and although there is reason to believe that true se.xual 

 products are formed by many of them, yet these develope themselves out of the general 

 substance of the body, instead of in distinct organs set apart for their evolution. Yet, as will 

 hereafter appear, these creatures perform all the functions which constitute in their aggregate 

 the life-history of an Animal. They obtain food either by moving actively in search of it, or 

 by putting forth prehensile appendages which bring it to them ; they introduce their food 

 into the interior of their bodies, and subject it to a process of digestion whereby its nutritive 

 material is extracted from the indigestible residue, which is cast forth by an act of defecation ; 

 they diffuse this material through the general substance of the body, both by the general 

 movements of its walls, and by the agency of what seems to be a special contractile organ ; 

 and they apply it to the augmentation of their own bodies by growth, and to the propagation 

 of their race by reproductive operations of various kinds. 



3. As less differentiation of parts exists among Rhizopoda than in either of the other 

 classes, and as the beings of which that class is composed may be considered as exhibiting 

 the distinctive attributes of Animal life in their least specialised condition, its place is obviously 

 at the bottom of the series. In fact, a state of greater simplification can scarcely be 

 conceived to exist in any living organism, than that which is presented by the creatures 



