388 GENERAL HISTORY OF THE INFUSORIA. 



sharp and thin ; dorsally they are separated by a shallow groove ; but along 

 the ventral line of the body the groove is deep and narrow, and the produced 

 edges of the lateral parietes resemble the valves of a bivalve shell. 



*' The ventral and dorsal grooves pass into one another in front ; but pos- 

 teriorly the lateral edges are united for a short space. The edge of the left, 

 less convex, side of the body ends anteriorly in an obtuse point, which cor- 

 responds with the anterior termination of the angulated ridge, and does not 

 extend by any means so far forward as the edge of the right side, which re- 

 mains thin, and forms the anterior extremity of the body. 



" At the anterior extremity, the large oral aperture 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 aper- 

 ture 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 apparatus 

 of hard parts situated on the opposite or ventral side of the mouth, and ex- 

 tending thence through two-thiixls of the length of the body. 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 ante- 

 rior portion ; but it would seem to be a deep ring, composed of three pieces — 

 two supero-lateral and mutually- corresponding, united with a third, inferior, 

 azygos portion. The latter is somewhat triangular, ^ith a broad base and 

 rounded obtuse apex, — the latter being directed forwards, and immediately 

 underlying the oral aperture, while the former is tiuned 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 expression either of 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 ap- 

 posed 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 ex- 

 tremity seems to taper to a fine point. Rather in front of the middle of its 

 inferior edge each style seems to give off a short process downwards ; and 

 this process is, in botanical language, deciuTent upon the style. Careful 

 examination of the dorsal or ventral aspect of these parts shows that the 

 decurrent process is, in fact, only the expression of a delicate membrane, which 

 is bent so as to have a ventral convexity, and connects together the two 

 styles. It might be said, therefore, that the posterior part of the apparatus 

 is a triangular membrane, deeply excavated in front, bent so as to be convex 

 downwards, and having its margins thickened and produced into styliform 

 enlargements. This curious piece of mechanism is directed upwards and 

 backwards, and terminates in the substance of the body without any apparent 

 connexion with other parts. 



*' The whole apparatus is moveable. The posterior portion is pushed against 



