Sub-Kingdom I. PROTOZOA 



PROTOZOA are unicellular organisms, with bodies consisting of sarcode (proto- 

 plasm), usually very minute, frequently microscopic in size, and without 

 differentiated tissues or organs. They are water-inhabitants, take in nourishing 

 matter either at any point on the periphery of the body whatsoever, or 

 through a so-called mouth (cytostome), and reject the undigested portions either 

 from any part of the body whatsoever, or from a definite point called the anal 

 aperture (cytopyge). The contractile sarcode almost invariably contains one or 

 more nuclei, and exhibits considerable diversity of structure and differentiation. 

 Locomotion is accomplished by means of vibratile cilia, flagella, pseudopodia, 

 or irregular processes of the periphery. Reproduction takes place by means of 

 budding or self-division, which latter process is often preceded by a temporary 

 coalescence (conjugation) of two individuals. Protozoa are divided into four 

 classes: Rhizopoda, Flagellata,- Infusoria, and Gregarina (Sporozoa), of which only 

 the first class is represented in the fossil state. 



Class 1. RHIZOPODA. 



Body-substance composed of richly granulated, jelly-like sarcode, which ttlfrni'ifi.'!/! 

 retracts, and again coalesces with irregular, finger-like, or thread-like 

 called pseudopodia. 



Rhizopods have been so named on account of the property they possess of 

 protruding pseudopodia from the periphery of the body. Although serving as 

 a means of locomotion and for the taking up of nutritive matter, the pseudo- 

 podia represent no permanent organs, since they are protruded only for the 

 I IMS- ing occasion, and disappear again as they coalesce with the main body of 

 sarcode. The pseudopodia often exhibit protoplasmic streaming, and occa- 

 sionally interlace so as to form networks. Rhizopods usually secrete calcareous, 

 silicious, or chitinous tests, or build silicious skeletons of exceeding great 

 diversity of form. Enormous deposits are built up by their accumulation 

 on the sea-floor, and numerous strata of marine origin are largely composed 

 of their remains. 



Four orders of Rhizopods are recognised: Forj^nifera, Ra^^ria, Amoebina? 

 and Heliozoa ; of these only the first two have parts capable of preservation. 



1 Butschli, 0., Protozoen in Bronn's Classen und Ordnungen des Thierreichs, 1880-1889. 



2 To the Amoebina, Huxley and Haeckel formerly assigned the so-called Bathybius, a reticu- 

 lated jelly-like substance composed of anastomosing strands, aiid occurring at great depths in the 

 Atlantic Ocean. Wyville Thomson and Moebius regarded it as a precipitate of calcium sulphate, 



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