A HANDBOOK OF 



PRACTICAL PARASITOLOGY. 



PART I. 



PROTOZOA. 



A. GENEEAL SURVEY. 



I. INTRODUCTORY : UPON THE ORGANIZATION OF THE PROTOZOA. 



THE Protozoa are single-celled animal organisms which may 

 attain to comparative complexity of structure, owing to the fact 

 that their body-parts vary according to the functions which they 

 are required to perform. These modifications do not, however, affect 

 the unicellular "form-value" of the organism, and for this reason 

 the modified processes of Protozoa are termed " cell-organs " or 

 " organelles/' to distinguish them from the true organs, built up 

 of many cells, of the Metazoa. The most important of these 

 organelles are as follows : 



1. Organelles of Protection and Support. 



(i.) Superficial Modifications. In the case of the greater number 

 of the Protozoa a viscid, hyaline, outer or ectoplasm (ectosarc) is 

 distinguished from a more liquid and granular inner or endoplasm 

 (endosarc). In many parasitic varieties, however, and especially the 

 cell-parasites, there is no differentiation of ecto- from endoplasm. 

 In others, the difference is too slight to maintain constancy and 

 distinction of form ; hence the changes in shape of the Amoebae. 

 Stability of form is maintained by means of a thickened outer layer 

 of plasm, and this is termed variously periblast (of Flagellates), 

 cuticle (of Gregarines), and pellicle (of Infusoria and soil Amoebae). 



(ii.) Axis-filaments occur in many of the Flagellates. Their purpose 

 is to maintain constancy of form. They are seen in Trichomonas, 

 Herpetomonas, and in several of the Trypanosomes. 



(iii.) Protective secretions of the protoplasm are frequently observed 

 in the parasitic Protozoa in the developmental stage at which they 

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