8 American Quarterly Microscopical Journal. 



tremities, to the triangular pieces B B of the compound 

 levers, composed on each side of the two pieces, B and C. 



From the point p, Fig. 3, along their straight parts, the lan- 

 cets are tubular, taking the form e seen in the section, Fig. 7, 

 their incurved edges lying in contact in the groove of the 

 sheath, Figs. 8 and 9, and forming a circular channel, a, be- 

 tween them, through which the poison is injected. Projecting 

 into the channel a are seen the valves (one at d. Fig. 7), which, 

 falling together, prevent the escape of the virus along the 

 outer sides of contact.* 



Along the inner margins of the groove, on each side and 

 following the curved arms of the sheath, are two T shaped 

 rails, Fig. 7 a, or guide-bars, which, exactly fitting into grooves 

 of similar form. Fig. 7 b, in the lancets, hold them firmly to 

 the sheath, and at the same time allow a free sliding motion 

 for their projection. 



Between each of the last fine teeth of the lancets is a small 

 canal extending outward from the central cavity, rather in- 

 distinctly seen at b b b b b, Fig. 1 1, which presents a very cor- 

 rect view of this part as shown under the microscope. 



The extent to which the lancets may be projected is limited 

 by the stop attached to each at p. Fig. 3, and extending nearly 

 across this cylindrical part of the sheath. 



The protrusion being arrested at the angle c, Fig. 3, formed 

 by the sudden contraction of the sheath at that point. 



This appendage also acts as a valve to check the flow of 

 poison through the channel between the lancets, as may be 

 seen by observing its structure in the greatly enlarged lateral 

 view, Fig. 5, and in the transverse section through both lan- 

 cets and sheath. Fig. 6. 



It consists of two nearly semi-circular pieces, Fig. 5, a e, at- 

 tached at their inferior angle to the lancet, the straight sides 

 being anterior. On this side, each piece is thick and chitinous, 

 but diminishes to a thin, flexible edge on the curved side. 



Both pieces are firmly braced and held in place by the heavy 

 curved piece b, extending from the straight side of both to its 

 solid attachment with the lancet. 



A section through the point at which the two pieces forming 

 this valve are attached, Fig. 6, shows an opening between them 



* By an unfortunate misunderstanding. Figs. 6 to 9 were inverted by the engraver. 



