20 



INTRODUCTION TO THE PROTOZOA 



In the ciliates there are two types of 

 nucleus which look different, and each 

 individual has at least one of each. The 

 niicronucleiis is relatively small; it di- 

 vides by mitosis at fission and apparently 

 controls the reproductive functions of the 

 organism. The ))iac runnel ens is relatively 

 large; it divides amitotically at fission and 

 apparently has to do with the vegetative 

 functions of the organism. Both these 

 nuclei appear quite homogeneous in com- 

 position in contrast to the vesicular nuclei 

 of other protozoa. 



LOCOMOTION 



Protozoa move by means of flagella, 

 cilia or pseudopods. A flagelhim is a 

 whip-like organelle composed of a central 

 axoneme and an outer sheath. The axo- 

 neme arises from a basal granule or 

 blepharoplast in the cytoplasm. The axo- 

 neme has been shown by electron micro- 

 scopy to be composed of 9 peripheral and 

 2 central fibrils. In some species a fla- 

 gellum may pass backward along the body, 

 being attached to it along its whole length 

 or at several points to form an nndulating 

 membrane. Flagella are found in the 

 Mastigasida and in the flagellate stages of 

 the Sarcodasida and Telosporasida. 



A cilium is an eyelash-like organelle 

 resembling a small flagellum. It has a 

 sheath, basal granule and axoneme. In 

 Paramecium and other forms, the axo- 

 neme is composed of 9 peripheral and 2 

 central fibrils. Cilia are found in the 

 Ciliasida. The less specialized ciliates 

 have large numbers of cilia which are 

 arranged in rows and beat synchronously. 

 In the more specialized ciliates, special 

 locomotory organelles have been devel- 

 oped by fusion of cilia. A cirrus is a tuft 

 of fused cilia embedded in a matrix. A 

 membranelle is a more or less triangular 

 flap formed by the fusion of two or more 

 transverse rows of cilia; membranelles 

 are found especially around the mouth. 

 An undulating membrane (not to be con- 

 fused with the undulating membrane of 

 flagellates) is formed by the fusion of one 

 or more longitudinal rows of cilia; they 

 occur in the oral groove of some ciliates. 



A pseudopod is a temporary locomo- 

 tory organelle which can be formed and 

 retracted as needed. There are four types 

 of pseudopod. A lobopod is a relatively 

 broad pseudopod with a dense outer layer 

 and a more fluid inner zone; lobopods are 

 found in the amoebae and some flagellates. 

 Afilopod is a slender, hyaline pseudopod 

 which tapers from its base to its pointed 

 tip; filopods tend to anastomose and may 

 fuse locally to produce thin films of cyto- 

 plasm; they contain no cytoplasmic gran- 

 ules. A tnyxopod [rhizopod, reticnlupod) 

 is a filamentous pseudopod with a dense 

 inner zone and a more fluid outer layer 

 in which cytoplasmic granules circulate; 

 myxopods branch and anastomose to form 

 complex networks which are used for 

 trapping food and also for locomotion; 

 they are found in the Foraminiferorida. 

 An axopod is a slender pseudopod which 

 projects from the body without branching 

 or anastomosing; it is composed of a thin 

 outer layer of fluid cytoplasm and an axial 

 filament composed of a fibrillar tube con- 

 taining a homogeneous core; axopods are 

 found in the Heliozoorida and Radiolari- 

 orida. 



Locomotion can also be effected by 

 bending, snapping or twisting of the whole 

 body. A number of protozoa employ this 

 method. 



There is still another type of locomo- 

 tion, gliding, exemplified by Toxoplasma, 

 Sarcocystis, coccidian merozoites, greg- 

 arines and Labyrintlinla, in which the body 

 glides smoothly along without benefit of 

 any apparent locomotor organelles, change 

 in shape or other visible cause. Kummel 



(1958) found by means of electron micro- 

 graphs that the outer surface of certain 

 gregarines {Gregarina cuneata, G. poly- 

 morpfia, Beloides sp.) is thrown into a 

 series of deep, microscopic folds which 

 he thought produce mucus. Beneath these 

 folds in the pellicle are fibrils which he 

 thought contract to move the organism 

 along a mucous track. Jarosch (1959) 

 thought that the gliding of Gregarina, 

 Euglena and various single-celled plants 

 is caused by superficial fibrils thrusting 

 against extruded mucus. Beams et at. 



(1959) found numerous ultramicroscopic 



