THE INFUSORIA 



363 



together. In some sedentary species, too, there is a secretion of a 

 mucous substance, frequently strengthened by foreign particles, 

 which serves as a protective tube or case. This may be auto- 

 thecalous (Fig. 83), when the tube of each individual is distinct, 



FIG. 2. 



Ophi-ydium eichornii, Ehrb., a colonial Peritrichan with a coenothecalous mucilaginous 

 test. British. Freshwater. Size of colonies about 4 mm. in length. 



or coenothecalous (Ophrydium, Fig. 2), when the secretions of the 

 individuals composing a colony form a common test perforated by 

 a series of tubes. 



A large number of the sedentary forms are epizoic. Some 

 species of Epistylis are found on the appendages or body wall of 

 Cyclops and other small Crustacea, 

 but in this instance the epizoic 

 habit does not appear to be neces- 

 sary, as the same forms may also 

 be attached to water weeds or other 

 objects. There are other genera, 

 however, which are only found 

 upon the bodies of living animals, 

 and seem to be dependent on their 

 host for suitable conditions of exist- 

 ence, such are Dendrocometes and 

 Spirochona on the gills of Gammarus, 

 Kentrochana on the gills of Nebalia 

 (Fig. 3), and Cothurniopsis on the 

 gills of Astacus. In these cases no 

 special modification of structure can 

 be attributed to the epizoic habit. 



A great many genera are ento 



ZOic in habit, being found Only in 



the intestines, bladder, or blood of 



other animals. The remarkable 



consistency with which some of these forms occur in a particular 



situation in only one species of host, is similar to the partiality 



FIG. 3. 



Kentrochona nebaliae, from the maxilli- 

 ides of Nebalia. Size about '04 mm. 



