PROTOZOA : INFUSORIA. 71 



plug, and it is provided with two tufts of long cilia, one on 

 each side. On one side of the protrusible disc is the oral 

 aperture, which is continued by a distinct and well-marked 

 gullet into a central ill-defined cavity. Both the entrance of 

 the gullet and the bottom of the central cavity are provided 

 with very long, actively vibrating cilia, some of which are 

 almost setiform. The entire granular contents of the abdo- 

 minal cavity undergo a constant though slow rotation. 



Carchesium is another form which is like Epistylis in consist- 

 ing of a number of calyces supported upon a branched pedicle, 

 but differs from Epistylis and agrees with Vorticella in the fact 

 that the pedicle is contractile. 



Stentor, or the trumpet -animalcule (fig. n, b), is another 

 common Infusorian which is closely related to Vorticella. It 

 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. In Vaginicola (fig. i r, 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 Infu- 

 sorian 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 Calenterata. 

 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 with a number 

 of radiating filamentous tubes, which are furnished at their 

 extremities with suctorial discs, and are capable both of exser- 

 tion and retraction. These retractile tubes both seize the prey, 

 and serve as vehicles for the ingestion of food ; hence the 

 term " polystome," or many-mouthed, has been proposed for 

 the order by Professor Greene. 



III. ORDER FLAGELLATA. This order comprises those In- 



