Physiology o/Haematopinus tenuirostris, Burnt. 87 



plied to the former and run in the same direction, but then 

 Lend towards one another, and finally run divergently. 



It remains to be shown how this simple mechanism acts to 

 push the rostrum out of the sheath. From the middle line of 

 the dorsal integument of the head, above the point of articu- 

 lation of the antennae, four muscles start on each side (figs. 4 

 and 9e) and attach themselves to the above-mentioned chiti- 

 nous bands a a. If then these muscles contract, the chitinous 

 bands a a are approximated to each other, and with them also 

 the bands b b, which latter will touch about c. By this ex- 

 ceedingly simple mechanism the sucking-tube, which lies 

 folded in the space between a and c (fig. 9), is pressed forth. 

 The booklets become erected; the prickle comes into action; and 

 the function of sucking begins. A factor of some importance 

 in the function of sucking has still to be noticed. In the ex- 

 tended state the sucking-tube is twice as long as when retracted. 

 The air which was contained in it is therefore diffused over 

 twice the space during protrusion. As, further, there is a firm 

 closure ate (fig. 9), there is produced in the extended sucking- 

 tube a more or less exhausted space, according as the tube did 

 or did not contain air before its protrusion. Consequently, 

 without any thing further, the blood will be forced from the 

 wound into the sucking-tube by the pressure of the external 

 air. The sucking-tube, however, is not inactive in this busi- 

 ness, seeing that, as a fine tubule, it carries upwards the fluid 

 blood by capillary action. But when the muscles from the 

 dorsal side cease, and at the same time those of the ventral 

 side, which, springing from the hinder part of the head run 

 forward to the middle part of the sucking-tube (fig. 4, t), begin 

 to act, the booklets lay themselves back and the sucking-tube 

 is retracted into the sheath. The space at c (fig. 9) is now 

 reopened. By the pressure of the retracted sucking-tube the 

 inhausted blood is driven through c into the oesophagus, and 

 thence by the independent movements of the latter passed 

 further on. 



The oesophagus follows immediately behind the sucking-tube 

 (fig. 8 a?). This is a fine tube which passes through the middle 

 and hinder parts of the head, penetrates into the thorax, and 

 then soon opens into the stomach. The membrane surrounding 

 the oesophagus is clear, and exhibits extremely fine transverse 

 striae. Besides this transversely striated membrane a struc- 

 tureless one also appears to be present. 



The stomach, that part of the digestive organs which ex- 

 tends from the oesophagus to the Malpighian vessels, is elon- 

 gated and not very broad. At its upper end it shows on each 

 side of the insertion of the oesophagus two dilatations, which 



