96 



ZOOLOGY 



SECT. 



Most of the Ciliata are naked, having no shell or other form of 

 skeleton ; but in a few forms the body is provided with a shell or 

 lorica, formed of a chitinoid material, and reminding us of the 



pen 



FIG. 73. Vorticella. A, B, living specimens in different positions , C, optical section ; D 1 , D-, 

 diagrams illustrating coiling of stalk ; El, E-, two stages in binary fission; E3, free zooid ; 

 FI, F-, division into mega- and mierozooids ; G 1 , G 2 , conjugation ; H 1 , multiple fission of 

 encysted form ; H-, H : *, development of spores ; ax. f. axial fibre ; cort. cortex ; cu. cuticle ; 

 c. vac. contractile vacuole ; d. disc ; gull, gullet ; m. microzooid ; mth. mouth ; nil. mega- 

 nucleus ; per. peristome. (From Parker's Biology.) 



similar structure found in so many of the Mastigophora. Some 

 (Fig. 7J, 4) have bell-like shells, variously ornamented, and in 

 others (Fig. 72, 1) the similarly shaped shell is perforated and 

 resembles the skeleton of some of the Radiolaria. A chitinoid 

 plate or operculum (Fig. 72, 2, op.) may be fixed to the edge of the 

 peristome, and, when the animal is retracted in its case accurately 

 closes the mouth of the latter, or a similar operculum (J) is 



