96 



ZOOLOGY 



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 



Fig. 73. — Vorticella. A, B, living specimens in different positions , C, optical section ; Di, D-, 

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

 F 1 , F-, division into mega- and microzooids ; G 1 , G-, conjugation ; H 1 , multiple fission of 

 encysted form ; H-, H 3 , development of spores ; ax. f. axial fibre ; cort. cortex ; cu. cuticle ; 

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

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



similar structure found in so many of the Mastigophora. Some 

 (Fig. 71, 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, #, 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 (-5) is 



