THE RADIATE CHARACTER. 139 



by the means of these muscles that the extrusion of the 

 polype takes place : these muscle-bands, drawing in 

 the membrane to a concave form, diminish the con- 

 tained space, which is already full, either with water, 

 or as I rather suppose with the vital juices ; the only 

 yielding part is the long body of the polype, 

 which accordingly is forced out through the proper 

 aperture. 



It is manifest that the radiate structure is becoming 

 a subordinate character in these zoophytes ; at least 

 so far as that character implies a perfect circular 

 symmetry. This Encratea for example has certainly 

 a dorsal aspect and a ventral one : the direction of 

 the intestinal canal, and the position of the excretory 

 orifice making sufficiently plain which is the former. 

 For from this arrangement, which is almost exactly 

 repeated in some of the tubicolous Rotifera, as 

 CEcistes for example, the oval orifice is gradually 

 brought lower down the back by successive stages in 

 Melicerta, Limnias, and Stephatioceros ; until in Mo- 

 nocerca, Furcularia, and Notommata among the 

 illoricate Rotifera, it attains the normal situation 

 which it holds in the higher animals. Hence I have 

 not scrupled to call this the dorsal side of the zoo- 

 phyte, in the preceding description. While on this 

 subject I may mention that Eucratea frequently 

 inflates the membranous integument just below 

 the anus, in a manner common to many of the 

 Rotifera. 



The ciliary action is doubtless in some measure 

 involuntary; but the tentacles have the power of 

 separate and voluntary movement. I observed an 



