ECOLOGY, COMMENSALISM AND PARASITISM 397 



the teeth and in the mouth; Endolimax nana (Wenyon and O'Con- 

 nor, 1917), one of the commonest amebae in man, and Iodoamoeba 

 butschlii (Prowazek, 1912). 



Parasitic Ciliata.— A considerable volume could be written on 

 the parasitic ciliates. This is attested by the many great mono- 

 graphs on limited groups of this class of Protozoa, e. g., on Opal- 

 inidae, Astomida, Oxytrichida, Ophryoscolecida, etc. Highly 

 spectacular life histories, such as those of Leishmania, Trypanosoma 

 and Plasmodium, and economic importance in connection with 

 human affairs are absent here. Absent also are the pathogenic 

 effects of parasites of the Endameba type or of biologically sig- 

 nificant adaptations to complete symbiosis which characterize the 

 Hypermastigida. Nevertheless the parasitic ciliates represent a 

 group which illustrate in high degree the phenomenon of commen- 

 salism with morphological differentiations which place them with 

 the most complex types of Protozoa and the most highly organized 

 types of single cells. 



Infection in all cases is contaminative and made possible by 

 protective cysts in which the fundamental organizations may 

 remain dormant for years. With the exception of Balantidium, 

 pathogenic effects in man are of little importance. By mere num- 

 bers, however, especially of ectocommensals, functional activity of 

 the host may be weakened or even suppressed as when gills, eyes 

 and skin are covered with cysts due to Ickthyophthirius multi- 

 filius. Entodiniomorpha, on the other hand, as commensals in 

 the forestomach of ruminants are interpreted as approaching the 

 symbiotic relationship of Hypermastigida in termites. Dogiel (1928) 

 estimates the number of ciliates in cattle as 50,000 in 1 cc. of rumen 

 contents and Ferber (1928) carries the number in sheep and goats 

 up to 900,000 in 1 cc. The ability of these ciliates to digest cellu- 

 lose and to build up albumin in their own cell bodies is indirectly 

 advantageous in the nutrition of their hosts through the added 

 supply of their body protein (Dogiel, Ferber, Reichenow-Doflein) . 



Morphological evidences of adaptation to an endocommensal 

 mode of life are shown (1) by degenerative changes, and (2) by 

 specializations for protection, adhesion, movement and multiplica- 

 tion. Modifications of a degenerative character are shown by the 

 absence of mouth in Opalinidae and the Astomida in general and 

 the substitution of saprozoic food-getting methods for holozoic 

 methods which are characteristic of the free-living ciliates. Opal- 

 inidae are not only mouthless but they also lack the dimorphic 

 nuclei — macronuclei and micronuclei— which are distinctive diag- 

 nostic features of the Infusoria. The method of fertilization by 

 copulation of gametes and not by conjugation also distinguishes 

 the Opalinidae from the majority of other ciliates. On these grounds 

 Metcalf (1923) proposed a classification involving the separation of 



