902 PROTOZOA AND OTHER ANIMALS 



four hours had disappeared, the eggshell bursting and the ciliates escap- 

 ing. Though the author stated decisively that the ciliate belongs to the 

 genus Glaucoma, the description and figure do not prove that system- 

 atic position. 



Along with the adaptation of free-living Protozoa to a symbiotic 

 environment, there should be considered a number of instances of a 

 secondary type of infection of associates in the same hosts. These have 

 been referred to as facultative parasites, from the standpoint of the 

 secondary hosts. Facultative parasitism of Heteyocineta janickii on the 

 oligochaete Chaetogaster limnaei, which occurs with the hypocomid 

 ciliate in the mantle cavity of snails, is described below (p. 940) . Theil- 

 er and Farber (1932, 1936) found Trichomonas miiris present with 

 considerable frequency in oxyurid nematodes in white mice, and divi- 

 sion took place in the intestine of the worms. They even found tricho- 

 monads in nematodes when the flagellates could not be demonstrated 

 elsewhere in the mice. J. G. Thomson (1925) found Giardia present 

 in abundance in all of hundreds of nematode worms, Vianella sp., from 

 a specimen of the South American rodent Vhcacia vhcacla. Although 

 he found no trophozoites or cysts of Giardia elsewhere in the intestine 

 of the rodent, he observed the flagellate from the nematode to be mor- 

 phologically identical with G. viscaciae Lavier. Graham (1935) found 

 Giardia in nematodes, probably Cooperia oncophora, from a bull; but 

 was unable to find the flagellates in the intestine of the bull. A com- 

 parison with G. bo vis Fantham would be of interest. As species of Giar- 

 dia are otherwise exclusively parasites of vertebrates, it is likely that the 

 nematodes with Giardia had, like those with Trichomonas, been sec- 

 ondarily infected with the mammalian flagellates. Flagellates can evi- 

 dently survive for long and even multiply in the worms, so that their 

 presence in them without simultaneous occurrence in the lumen of the 

 vertebrate intestine is not significant. 



Systematically Related Free-living and 

 Symbiotic Protozoa 



mastigophora 



In addition to the existence of accidental and facultative parasitism, it 

 is significant in connection with the origin of symbiotic relationships 



