ECTOPARASITIC PROTOZOA 25 



discussed; however, the works of Entz (1912), Kiernik (1909) 

 and Wenrich (1924a) are especially valuable as guides to similar 

 studies. 



Comparative morphology: The works of James-Clark (1865) 

 and Kepner and Pickens (1925) are especially helpful as guides 

 to a comparative morphological study of the peritrichous ciliates. 

 This phase of study has been inadequately investigated. It offers 

 abundant material to one conversant with the general structure of 

 protozoa. 



Cytology: Wermel (1925) has made a very careful cytological 

 study of Hydr amoeba hydroxena. This is an exceptionally good 

 paper, but it is not readily accessible. A similar paper on the free- 

 living protozoa might serve equally as well to guide one in a 

 cytological study. 



Nuclear division and cndomyxis: Diller (1928) has described 

 endomyxis in TricJwdina from tadpoles. Neresheimer (1908) de- 

 scribes the origin of daughter nuclei from the principal nucleus in 

 the development of Ichthyophthirius. The author has recently 

 worked out the different stages in nuclear division of Hydramocba 

 hydroxena. This line of investigation promises sure results and is 

 especially recommended to the young investigator. 



Life-history studies: Control measures are based primarily on a 

 careful knowledge of life-histories. With the exception of Ich- 

 thyophtJiirius multifiliis (Fouquet, 1876) this knowledge of the 

 ectoparasitic protozoa is inadequate. In undertaking such prob- 

 lems efforts should be made to culture the organisms on artificial 

 media, as well as to make the study under natural conditions. 



Symbiosis: Caullery and Mesnil (1915) have described an alga 

 as living symbiotically with Trichodina patellae and Faure-Fremiet 

 (1909) describes an epizoic spirillum and an internal bacterium 

 living symbiotically with Trichodina pediculus. It is probable that 

 the presence of these symbionts enables the protozoa to withstand 

 certain conditions which otherwise would be unfavorable. 



Effect of protozoa on host: It is not unusual for ectoparasitic 

 protozoa to cause the death of their host. The pathogenic forms 

 most commonly found belong to the holotrichous cihates. Among 

 these Ichthyophthirius multifiliis deserves first consideration. 

 Dorier (1926) reports a very fatal skin disease of fish caused by 

 Enchelys parasitica. Apparently no one has conducted carefully 

 controlled experiments designed to show exactly what role the 



