VORTICELLA 



139 



undulating membrane. There are no cilia elsewhere upon 

 the body. 



The general character of the ectoplasm and endoplasm is 



the same in Vorticella as in Paramecium, but 



Ectoplasm the pellicle of the bell-animalcule is sculptured 



and Endo- c . , . , . r , 



plasm. in various ways according to the species, and 



below it is a distinct alveolar layer. Just under 

 the alveolar layer, in the walls of its bubbles, is a layer of 

 very fine contractile fibres or myonemes. Near the stalk the 

 ectoplasm is much thickened and the myonemes pass 

 inwards through it to join in the middle, where they form 

 a central contractile fibre which, with a covering of ectoplasm, 



'^S^SS^^^J^ki^ 



Fig. 85. — A group of individuals of Vorticella 

 in various phases of the life-history. 



a., Ordinary individual ; 3., the same contracted ; c, 

 ordinary fission ; d. , a later stage of the same ; e ., 

 free-swimming individual produced by ordinary 

 fission \f., /'., two modes of fission to form a con- 

 jugant ; £-., conjugation. 



makes up the stalk. This is enclosed in a cuticular tube 

 formed by secretion. The contractile fibre is not quite 

 straight, but lies in a very open spiral, so that when it 

 contracts it draws the stalk into a close coil. There are no 

 trichocysts. The endoplasm is granular. 



