4/2 ON DYSTERIA 



obtuse point {in), which corresponds with the anterior termination of 

 the angulated ridge, and does not extend, by any means so fcr forward, 

 as the edge of the right side, which remains thin, and forms the 

 anterior extremity of the body. 



At the anterior extremity the large oral aperture {a) is seen, just 

 below the angulated ridge and occupying the bottom of a deep fossa, 

 which here takes the place of the dorsal and ventral grooves. The 

 left wall of this fossa is thickened, and projects inwards so as to form 

 a cushion-like lobe, clothed 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 having 

 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 distinguishable ap- 

 paratus 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 apposition with a much elongated, styliform, posterior portion. 



It is very difficult to assure oneself of the precise structure of the 

 anterior portion (/), but it would seem to be a deep ring, composed of 

 three pieces — two supero-lateral and mutually corresponding {q, fig. 

 14), united with a third, inferior, azygos portion (/). The latter is 

 somewhat triangular, with a broad base and rounded obtuse apex ; 

 the latter being directed forwards and immediately underlying the 

 oral aperture, while the former is turned backwards, and unites with 

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

 and convex externally, so as to form a segment of a circle, and pre- 

 sents a clear median space, the optical expression of either a per- 

 foration 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 two styles, which are somewhat like nails in shape ; their 

 anterior extremities being truncated so as to present a sort of nail- 

 head, while the posterior extremity seems to take to a fine point. Rather 

 in front of the middle of its inferior edge each style seems to give off 

 a short process downwards {s), and this process is, in botanical lan- 

 guage, decurrent upon the style. Careful examination of the dorsal 

 or ventral aspect of these parts shows that the decurrent process is in 



