HUXLEY, ON DYSTERIA. 79 



with remarkably long cilia ; and these cilia are continued 

 into the oral aperture itself — the posterior ones being large, 

 usually directed transversely to the axis of the body, and 

 ha^dng at times much the appearance of vibratile membranes. 



The bottom of the oral fossa is strengthened by a curious 

 curved rod (/), which terminates superiorly in a bifid tooth, 

 while inferiorly it appears to become lost in the wall of the 

 fossa. 



But there is a much more prominent and easily distin- 

 guishable apparatus of hard parts situated on the opposite 

 or ventral side of the mouth, and extending thence through 

 two thirds of the length of the body {b, c) . It consists of two 

 portions — an anterior, somewhat rounded mass, in appo- 

 sition with a much elongated, styliform, posterior portion. 



It is very difficult to assure oneself of the precise structure 

 7 of the anterior portion ;(/), but it would seem to be a deep 

 > ring, composed of three pieces — two supero-lateral and mu- 

 tually corresponding (y, fig. 14), united with a third, inferior, 

 azygos portion {p) . The latter is somewhat triangular, with 

 a broad base and rounded obtuse apex ; the latter being 

 directed forwards and immediately underlying the oral aper- 

 ture, while the former is tiu*ned backwards, and unites with 

 the two supero-lateral pieces. Each of these is concave inter- 

 nally and convex externally, so as to form a segment of a 

 circle, and presents a clear median space, the optical expres- 

 sion of either a perforation or of a much thinned spot. 



The anterior edge of each supero-lateral piece is nearly 

 straight, but the posterior is convex, and it is by this edge that 

 it articulates with or is apposed to, the anterior extremity of 

 the posterior division of the apparatus. Viewed laterally this 

 posterior portion appears to consist of tAvo styles, which are 

 somewhat like nails in shape ; their anterior extremities being 

 tnuicated so as to present a sort of nail-head, while the 

 posterior extremity seems to take to a fine point. Rather in 

 fi'ont of the middle of its inferior edge each style seems to 

 give off a short process doAvnwards {s), and this process is, in 

 botanical language, decurrent upon the style. Careful ex- 

 amination of the dorsal or ventral aspect of these parts shows 

 that the decurrent process is in fact only the expression of a 

 delicate membrane, Avhich is bent so as to have a ventral 

 convexity, and connects together the two styles (fig. 15). It 

 might be said, therefore, that the posterior part of the appa- 

 ratus is a triangular membrane, deeply excavated in front, 

 bent so as to be convex doMTiwards, and having its margins 

 thickened and produced into styliform enlargements. This 

 curious piece of mechanism is directed upwards and back- 



