OF WASHINGTON. 275 



lower surface. It is covered by a very thick chitinous integu 

 ment and is connected at its posterior border with the body by a 

 broad and short muscular band, the pedicel, by which it is en 

 abled to move on this axis only upward and downward. Its supe 

 rior surface presents a subtriangular form, as the centre of the an 

 terior border is drawn out into a sheath-like prolongation in which 

 the basal parts of the mandibles are concealed. 



The lateral sides are either straight or drawn out into a more 

 or less prominent point, as in Boophilus and Rhipicephalus. 

 The posterior border is generally straight or slightly emarginate, 

 and often strengthened by an elevated chitinous ridge, while the 

 posterior lateral corners are frequently drawn out into a more or 

 less prominent spine-like process. Upon the dorsal surface we 

 notice, especially distinct in the female, two small circular and 

 impressed spots side by side which are generally of a lighter color 

 and coarsely punctured. These have been by some writers 

 (Kolenati) considered as the eyes. 



At the underside the basal piece is generally a little longer than 

 at the dorsal side, and we notice here a transverse line dividing 

 the surface into halves. 



The morphological character of this basal piece has, by various 

 writers, been differently explained. I hold, however, with Koch 

 and Pagenstecher that this organ is formed by the coalescence of 

 the labrum above with the labium and mentum below. The 

 larger size and the visible dividing line speak in favor of this 

 view. 



The rostrum or proboscis is of an elongate form and extends, 

 in the young ticks, horizontally forward ; in the mature stage, 

 however, it projects downward at an angle. It consists of those 

 organs which serve to pierce the skin of the host and to draw its 

 blood. It is composed of the mandibles and the maxillae in their 

 peculiarly modified forms (suiting a life as a parasite) , the former 

 lying closely with their underside upon the upper surface of the 

 latter, forming thus apparently one piece. The maxilla? at their 

 upper or inner surface are excavated longitudinally, and as the 

 underside of the mandibles is also concave to near the tip, a 

 channel is thus established through which the blood passes into 

 the stomach. This fact, although easily made visible by cross- 

 sections, has never been observed before, and is emphatically de 

 nied by Pagenstecher. 



