PROTOZOA AND OTHER ANIMALS 903 



that certain genera contain both free-hving and symbiotic species, or 

 that the two types of habitat are occupied by members of closely related 

 genera. The organisms have become closely adapted to their biotic en- 

 vironment, but have not undergone extensive modification. That does 

 not necessarily imply recent adaptation, since stability of characteristics 

 would equally well explain it; but it does indicate a direct origin from 

 free-living types. 



There are some epibiotic euglenids, including species of Ascoglena 

 and Colacium, Euglena cydopkola described by Gicklhorn (1925), and 

 Euglena parasitica described by Sokoloff (1933). The last species ad- 

 hered by the anterior end to all of numerous colonies of Volvox in a 

 tank in Mexico City, and was not found free in the water. In the 

 green color, stigma, and other structures, except for lack of a flagellum, 

 this is a typical Euglena. It is not certain, however, whether the relation- 

 ship is more than occasional phoresy. E. cydopkola is normally epibiotic, 

 occurring on Cyclops strennuus and species of Daphnla. Epibiotic eug- 

 lenids have been observed on plankton Crustacea in reservoirs in the 

 vicinity of Berkeley, California. 



The euglenids, Euglenamorpha hegneri, E. pellucida. and Hegneria 

 leptodactyli, are obligate inquilines of amphibia. They have never been 

 found free-living. Species of Euglena and Phacus, with normal green 

 color and activity, have, however, been found living in frog tadpoles 

 (Alexeieff, 1912; Hegner, 1923; Wenrich, 1924a). This is merely a 

 survival of free-living forms in the intestine, and Alexeieff may be un- 

 justified in terming it facultative parasitism. A colorless euglenid of the 

 genus Menoidium was found living in the intestine of one specimen of 

 Sphoholus marginatus by Wenrich (1935); and it occurred free-living 

 in damp Sphagnum in the aquarium jar. He reported no observations on 

 how long this flagellate might survive in the host. Euglena gracilis fed 

 to the millipeds could be in part recovered alive in one or two days. 



Euglenamorpha hegneri Wenrich was observed by Hegner (1922) 

 and described by Wenrich (1923, 1924a) and Hegner (1923) from 

 tadpoles of frogs and toads and from Hyla in the North Atlantic states. 

 The typical form has green chloroplasts, a red stigma, and three flagella. 

 In 0.6 percent salt solution it survived for weeks in a hanging drop, 

 and multiplied at first, but continued cultivation was not achieved. A 

 colorless form, distinguished as the variety pellucida by Wenrich, is also 



