20 



RESEARCH IN PROTOZOOLOGY 



rapidly undergoes approximately eight successive divisions, thus 

 giving rise to a large number of daughter nuclei. Each daughter 

 nucleus becomes associated .with a mass of cytoplasm and de- 

 velops into a small ciliate which attacks a new host. 



In addition to the injury caused by a loosening of the epidermis, 

 the ciliates prepare the way for an invasion of the tissues by 



^/,//////V^ 



fv ' %h PC 



B y^),\ 



aU^^^y.^ 



Fig. 5. — A, Trichodina pediculns; B, T. steini. (cv) contractile vacuole; 

 (/t;), food vacuoles; (n) macronucleus ; (pc), peristomial cilia; (v), velum. 

 X 250. (A modified from James-Clark; B after Kepner and Pickens.) C, 

 Prorodon teres. The protozoon has ingested the end of a Hydra's tentacle; 

 three food vacuoles and a contractile vacuole are shown. X about 50. (Modi- 

 fied from Reukauf.) 



bacteria and fungi. In this way they may be indirectly the cause of 

 more serious injury than they themselves produce. In some cases 

 the ciliates accumulate on the gills of a young fish in such numbers 

 as to cause suffocation. 



Conditions favorable to the parasites are high temperature and 

 insufficient water flow. It is not easy to kill the parasites while 



