338 BIOLOGY: GENERAL AND MEDICAL 



Among animal organisms nearly every phylum has 

 its parasitic representatives. They are most numerous 

 among the most simple organisms and occur with dimin- 

 ishing frequency as the scale of life is ascended until, 

 when the vertebrates are reached, there is but a single 

 representative. 



The following systematic arrangement of the parasitic 

 forms is founded upon the excellent paper upon the sub- 

 ject in the New International Encyclopedia. 

 Phylum Protozoa. 



Class Rhizopoda. These include the amoeba, 

 of which many species are parasitic in the 

 alimentary tracts of many other animals. The 

 most important is the Entamceba histolytica 

 Schaudinn, that causes tropical dysentery 

 in man. 



Class Infusoria. These are ciliated organisms 

 like Balantidium coli of man. Trichodinse is a 

 parasite of the gills and gill cavity of the frog; 

 Opalina, of the bladder and gut of the frog; 

 Holophyra, an epiparasite of certain fish; Ancis- 

 trum infests the mantle cavity of certain mol- 

 lusks; Anophlophyfa occurs in the intestines of 

 certain marine invertebrates. 

 Class Mastigophora. These are flagellate or- 

 ganisms like Trichomonas intestinalis, Tricho- 

 monas vaginalis, Cercomonas intestinalis, and 

 Megastoma entericum. They also include a 

 number of alimentary and blood parasites, such 

 as Herpetomonas, and true blood parasites, 

 such as the Trypanosomes, many of which are 

 dangerous or fatal parasites of man and the 

 lower animals. 



Piroplasma or Babesia and the Leishmania may 

 also belong to this group. Many are harmful 

 and fatal parasites of man and the lower ani- 

 mals. 



