390 



BIOLOar OF THE PROrOZOA 



:j 



laterals, anals and caudals and there is a reduction in the ninnber of 

 uniform ventral cilia corresponding to the increased number and 

 complexity of the cirri. Thus frontals appear as the only differenti- 

 ated motile cirri in some species of the Urostylifhe, frontals and anals 

 in other species, while the remainder of the ventral surface is clothed 

 with uniform cilia. Cirri are increased and ventral cilia further 

 reduced in the Family Pleurotrichid^e, and 

 •fC" "^""^ !n^ ventral cilia are entirely lost in the family 



iV" .; '^^ Euplotidje and in Aspidiscida^. 



1^-' \ ' vf The hypotrichs arerareh' parasitic {Kerona 



on Hydra); a few are tube-dwelling (Sticho- 

 tricha. Fig. 173), but the great majority are 

 bottom feeders with characteristic creeping 

 movement on their cirri, or with sudden 

 springing movement due to the activity of 

 the usually more powerful anal cirri. 



Nuclei are usually multiple, two macro- 

 nuclei and two micronuclei being the rule; 

 conjugation and encystment occur in all 

 forms, and, so far as known, reorganization 

 is characteristic of both phenomena. Cysts 

 are frequentl^' ornamented by numerous 

 spines. The six families are distinguished, 

 in the main, by the arrangement and special- 

 ization of the A-entral motile organs. 



Fa mill/ 1. Peritromidae, Stein.— Flattened 

 forms with coating of iniiform and undiffer- 

 entiated cilia on the ventral surface; the 

 adoral zone follows the anterior margin. 

 One genus— /Vr///'o///?/.s', Stein Fig. 172, B). 

 Famihi 2. Urostylidae.- This group differs 

 from the more generalized Peritronms in the 

 differentiation of the frontals while anal cirri 

 may or may not be present. Ventral cilia 

 are present in all forms. Some are ecto- 

 parasitic {c. g., Kerona pediculus, Fig. 79, 

 p. 151, on Hydra) but the majority are free- 

 living in stagnant water. Characteristic 

 genera are given below; see Key for full list. 

 Anal cirri are present only in the genera: 



1. Arnyhisia (Fig. 175), with 2 to 3 rows of ventral cilia, 2 mar- 

 ginal rows. 



2. Urostyla, with 5 to 7 rows of ventral cilia, 2 marginal rows. 

 Three to several frontal cirri, but no anal cirri are present in: 



3. Trichogaster, with ventral surface covered with fine cilia. 



:t: 



Fig. 173.— Stichotricha 

 secunda, a tube-dwelling 

 hypotrichous c i 1 i a t e. 

 (Original.) 



