494 



PEOr. ALLMAN ON THE STErCTUEE AlO) 



ring here along the middle line o£ the tentacle ; these are ar- 

 ranged in groups of two or three at tolerably regular intervals. 



"While the outer cellular layer of the body- wall is thus carried 

 over the back of the tentacles, their opposite or oral side is clothed 

 by a continuation of the ciliated epithelium of the mouth. Besides 

 the cilia thus continued from the mouth along the middle line of 

 the oral side of the tentacles, there is a dense* line of vibratile 

 cilia along each of the opposed sides of the tentacles. On each 

 side of the ciliated tract which runs along the middle of the oral 

 face of the tentacle and between this tract and the lateral line of 

 cilia is a non-ciliated area which, according to Nitsche, carries a 

 series of long stiff bristles. These stand singly at regular dis- 

 tances from one another and tolerably close, thus differing from 

 the bristles on the back of the tentacles, which are disposed in 

 groups of two or three. 



The inner epithelium extends from the cavity of the lophophore 

 into that of the tentacle, and presents two strong ridges, one along 

 each of the lateral sides of the tentacular lumen. 



Special Muscles. — The investigation of specimens hardened in 

 chromic acid shows in the interior of the tentacles two fasciculi 

 composed each of two or three long fibres. These had been 

 already noticed by Hyatt, and their existence is now confirmed 

 by Nitsche. They run, one along the oral side, the other along 

 the opposite side of the tentacle. Their fibres contain nuclei and 

 are apparently muscular. 



The same homogeneous membrane already so frequently re- 

 ferred to has been followed by Nitsche into the epistome, where it 

 forms the foundation-layer of this organ. Hyatt describes three 

 muscle-bands as entering into the structure of the epistome. I 

 had already described the musculature of the epistome as con- 

 sisting of a single strong fasciculus which acts as an elevator*. 

 With this view the observations of Nitsche are entirely in ac- 

 cordance. 



Under the name of " brachial contractors," Hyatt describes a 

 series of previously unnoticed muscular bands situated within the 

 arms of the lophophore, where they run transversely in their walls. 

 These, by their contraction, act on the floor of the arms, drawing 

 it up into folds. 



He also, under the name of lophophoric flexors," describes 

 ' Monograph of the Freshwater Polyzoa.' 



