138( s - s -440) THE MONONCHS 



areas, armed with minute denticles arranged in transverse rows like the 

 teeth of a rasp (subgenus Mylonchulus 6 ). While these denticles are 

 usually distributed in two distinct areas, the two sometimes coalesce on 

 the ventral line, so that the denticulated area, or rasp, is continuous and 

 bilaterally symmetrical. As a rule, however, there is a distinct, narrow, 

 ventral interruption, so that the right and left rasps are rather clearly 

 separated from each other. These rasps are widest near the ventral line, 

 and become gradually narrower as they recede, and usually end near the 

 lateral line, or near the dor sally submedian line. On the margins of the 

 rasps the denticles are arranged in distinct rows ; elsewhere the arrange- 

 ment is more or less irregular, though in certain species the arrangement 

 is rather orderly throughout. Each rasp is composed of about six rows 

 of denticles, except in the species denticulatus, where the number of rows 

 is about twice (?) as great, and in the new species sparsus and reversus, 

 where there are only one or two rows. Often at the base of each rasp 

 there is an exceedingly minute submedian onchus. 



Method of Attack. When used in conjunction with the strong dorsal 

 tooth and the powerful lips, the rasps are remarkably efficient organs. 

 The mononch glides up to its quarry and makes its onslaught by a quick 

 snap of the head, throwing its jaws suddenly wide open, and grappling 

 its prey by means of the inner armature of the lips. As the jaws close in, 

 the victim's body is jammed against the point of the dorsal tooth, as well 

 as against the rasps, and in this way is at once both punctured by the tooth 

 and lacerated or milled by the rasps. In most cases the onchi seem to be 

 solid bodies, containing no duct through which venom could empty. If 

 any poison is injected into the victim it would seem to be derived from 

 cesophageal glands emptying into the pharynx by some other road. The 

 axial element sometimes seen in the onchus is probably a nerve ending. 



Minutia of the Wall of the Throat. In general the wall of the pharynx 

 is well developed and strongly refractive, and is usually thickest on the 

 dorsal side where it gives support to the dorsal onchus ; often it is very 

 finely transversely striated. In many species this striated appearance 

 seems to be due to a transverse lamination of the pharyngeal wall. The 

 striation, or lamination, may be so pronounced as to give rise to transverse 

 ridges on the interior surface of the pharynx like those of the teeth of a 

 mill-saw file, and no doubt these ridges have somewhat the same function 

 as the rasps just described. The onchi are sometimes seen to be longi- 

 tudinally striated. The striae of the pharyngeal walls are most clearly visi- 

 ble during the moulting period. In the original species-figures to follow, 

 what appears merely as shading on the pharyngeal wall is a carefully 

 worked-out chart of the position, number and direction of these lami- 

 nations. 



8 Mylonchulus, a small mill-tooth. 



