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MANUAL OF ZOOLOGY. 



but differs from Epistylis and agrees with Vorticella in the fact 

 that the pedicle is contractile. 



Stentor, or the trumpet-animalcule (fig. 16, b\ is another 

 common Infusorian which is closely related to Vorticella. It 



Fig. 16. a Vaginicola crystallina ; b Steutor Mulleri ; c Group of Vorticellce ; 

 d Detached bud of Vorticella, showing the posterior circlet of cilia. 



consists of a trumpet-shaped calyx, devoid of a pedicle, but 

 possessing the power of attaching and detaching itself at will. 

 When detached it swims by means of the anterior circlet of 

 cilia, just as the calyx of Vorticella will, if broken from its 

 stalk. True muscular fibres appear to be present in the cor- 

 tical layer of Stentor. In Vaginicola (fig. 16, a) the essential 

 structure is much the same as in Vorticella, but the body is 

 protected by a membranous or horny case (" carapace " or 

 " lorica "), within which the animal can retire. In this beautiful 

 Infusorian the carapace is certainly a cuticular secretion, but 

 it appears at the same time to be quite distinct from the true 

 cuticle itself. 



Amongst the structures of the Infusoria which require some 

 notice are the "pigment spot" and the " trichocysts." The 

 pigment spot is a brightly-coloured solid particle, generally 

 red, of very common occurrence in many Infusoria, but of 

 quite unknown function. The " trichocysts " are vesicular 

 bodies, capable of emitting thread-like filaments, and greatly 

 resembling the urticating cells of many of the Ccelenterata. 

 They have been detected in Bursaria, as well as in various 

 other members of this order ; and they are very like certain 

 cells which are found in the integument of many Planarians. 



II. ORDER SUCTORIA. This order includes a series of In- 

 fusoria of a very anomalous nature. In Acineta,* which may 

 be taken as the type, the body is covered wi.th a number 



