CILIATA. 



199 



one or more rings of large cilia round the edge of a raised lid- 

 like flap which is capable of being shut down. There is also an in- 

 ferior row of cilia upon this flap running to the 

 mouth. The free-swimming Infusoria often 

 possess in addition to these delicate cilia and 

 zones of cilia, thicker hairs and stiff bristles, 

 and more or less bent hooks, which are em- 

 ployed in locomotion and for attachment. 



Certain fixed Infusoria as Stentor (fig. 138) 

 and Cothumia secrete external coverings or 

 shells, into which they retract themselves. 

 Nourishment is taken in in a few cases by 

 endosmosis through the whole surface of the 

 body, e.g., the parasitic Opalina.. The Acineta 

 feed themselves by sucking the body of their 

 prey. They are without a mouth, and are 

 incapable of taking in solid food. But they 

 possess a number of long, narrow, contractile 

 tentacles, which radiate from the surface of 

 their bodies, and have the form of delicate tubes, 

 presenting a structureless external wall and a FIG. 133. Stentor 

 semi-fluid granular axis. The Acineta applies ^ <* a * t %k 

 one or more of these organs to the body of an gullet; pv, pulsating 



, i . -i T , P vacuole : N, nucleus. 



extraneous organism, when the substance of 



the latter travels down the interior of the granular axis of the 



tentacle into the body of 



the Acineta (fig. 139). 



By far the greatest num- 

 ber of Infusoria possess an 

 oral aperture, usually near 

 the anterior pole of the 

 body, and a second aperture 

 which acts as anus, and 

 which can be seen in a 

 definite part of the body as 

 a slit during the exit of the 

 excreta. 



The bodv mrenohvim' FlG ' 139 ^"''' tt /<,.r?;m Ehrbj?., which in 

 eUJina, sucking the body of a small i nfusor i a n (Enchelys) 



which is bounded by the (after Lachmann). T, sucking tentacle ; V, vacuole ; 



external membrane, is N> 



divided into a viscid exoplasm and a more fluid endoplasrn, into 



