176 PARASITISM 



it is conceivable that the entire group of the hemosporidia may. have 

 been thus evolved from the flagellated protozoa, as the majority of 

 protozoologists now suspect, the evidence, as Schaudinn, Minchin, 

 Liihe, Hartmann, and others admit, being supported by the casual 

 formation of flagella-like structures in different species of the malaria 

 organism and the peculiar thread or pseudopodium-like appendage 

 of Babesia canis [Nuttall and Graham-Smith ('06), Patton ('07), 

 Kinoshita ('07)]. This evidence, however, is not strong enough to 

 justify far-reaching changes as yet in the well-established system of 

 classification, and we cannot support Hartmann, Sambon, Manson, 

 and other recent contributors in their attempts to do away with the 

 old group of hemosporidia. Hartmann's ('07) group of "binucleata," 

 including hemosporidia and the binucleated flagellates, is premature, 

 misleading, and demoralizing, and on the present evidence would be 

 no more justified than a zoologist would be justified in classifying 

 pisces and batrachia together in one group on the strength of the tad- 

 pole larva. In each case the vanishing structures show no more than a 

 suggestion of a possible relationship. 



In other cases of parasitic protozoa the cellular structures are prac- 

 tically identical with those of the nearest allied free-living forms. 

 Balantidium, opalina, biitschlia, dasytricha, and other ciliated para- 

 sites show unmistakable resemblance to the infusoria; pyrsonympha, 

 triclionympha, and some others a less perfect resemblance. Ameboid 

 parasites like Eniamcha histolytica, E. coli, or Chlamydophrys stercorea 

 are similarly related to the rhizopods. 



Like parasitic worms and moUusks, these parasitic forms may 

 become highly modified by their parasitic mode of life, and suckers, 

 hooks, spines, and other attaching organs may be well developed. 

 Such changes in cell structure may be the outcome of the specific mode 

 of life of the parasite and their methods of nutrition. Some of them, 

 like the majority of motile forms in the fluids of the digestive or cir- 

 culatory system, absorb their food as saprophytes do, by osmosis; 

 others, like the gregarines, triclionympha, pyrsonympha, and others, 

 have especially adapted attaching or feeding organs which may 

 act as haustoria to absorb food from the fluids of the host (e. g., 

 pyxinia. Fig. 73). 



The parasitic forms may be divided for descriptive purposes into 

 minatural groups, according to their modes of life. Some are purely 

 enterozoic, spending the entire life in the lumen of the digestive tract 

 {'flagellates like copromonas, cercomonas, herpetomonas, crithidia, 

 etc.); others are coelozoic, dwelling in the coelomic cavities of the body 

 (many gregarines); others are cytozoic, living throughout the vegeta- 

 tive period of life as intracellular parasites (coccidiidia, in epithelial 

 cells; myxosporidia, in muscle cells; and intracorpuscular hemo- 

 sporidia) ; still others are caryozoic, passing into the cell body to find 



