ANATOMY OF OPHIOTHEIX VARIABILIS, ETC. 



Ill 



shaped space exists leading to the two large papillae which come 

 next to the true teeth. It is evident that whilst the two papillae 

 just noticed can come in contact by their free edges with those 

 of the opposite jaw-plates, none of the other papillae can ever 

 touch their opposite and similar structures. 



The tooth-papillae do not therefore form any part of what has 

 been inelegantly termed a " chewing-apparatus." 



On removing the jaw-plate from the mouth-frames the adoral 

 surfaces of the jaws are seen side by side (fig. 8). Each jaw sur- 

 face is tall from below upwards, narrow from side to side, hollow 

 along the median line inferiorly, and with four irregular depres- 

 sions in the upper part. 



The four depressions correspond to the four foramina of 

 one side of the jaw-plate, and the long hollow with the aboral 

 surface of the jaw-plate on one side of the median line. The 

 depressions give attachment to the muscles which pass through 

 the foramina of the plate and are attached to the bases of the 

 teeth (fig. 3). The long hollow below is for connective tissue 

 which unites the converging jaw-ends and also the jaw-plates, 

 and the groove of the hollow is completed by the approximation 

 of the jaws. But there are about seven minute hollows or pits on 

 the interradial side of each jaw, close to the projecting part which 

 is in contact with the jaw-plate, and as many minute grooves 

 pass from them over the edge and reach the long hollow. They 

 appear to have no connection with the seven side tooth-papillae, 

 and they give attachment to muscular fibres (interradiales 

 adorales inferiores) and connective tissue which bind the side of 

 the jaw-plate to the jaw. It is possible that slight sliding 

 movements of the jaw T -plate upon the jaw-ends are thus rendered 

 possible. It is evident that the duty of the muscles (inter- 

 radiales adorales superiores) w T hich pass through the foramina is 

 to make the teeth stick out from the jaw-plate perpendicularly 

 to it, and allow r them to move slightly upwards or downwards at 

 their free edge during the period when contraction does not 

 occur. Chewing is, however, not possible, but the process of 

 filtering occurs. 



III. The Radial Shields, Genital Plates, Scales, and Muscles. 



The aboral end of the radial shield is rather narrow 7 , is slightly 

 separated from that of the other shield, and projects over an 

 aboral ridge of the genital plate, and both are placed well over the 



