81 



are relaxed and the natural elasticity of the plunger brings it back 

 to its position at rest and forces the saliva out through the syringe- 

 stem (ps). The fold of the barrel-wall is in such intimate contact as 

 to appear but one pièce, but it is really composed of two 

 layers, as shown at V, fig. 1. The arrows indicate the direction 

 of the stream of saliva. The wall of the syringe-barrel is of heavy 

 chitin : the posterior end invaginated and of thinner and flexible 

 chitin, forming the plunger; the small, rounded end of the 

 latter is solid and heavily chitinous, and from it the plunger-rod 

 (pr),alsostrongly chilinised, projects posteriorly andgradually thins 

 out until it becomes a mère tendon in the niidst of the retractor 

 muscles. At its anterior end the syringe-barrel suddenly narrows 

 into the stem, a hollow chitinous tube strengthened on the lower 

 side by the thick rib (r). This tube or salivary duct opens at its ante- 

 rior end on the upperside of the base of the labium (bl) beneath a 

 little tongue or valve (t) which lies betvveen two thickened strips 

 formed by the ends of two struts (st) from the tentorium. The 

 whole apparatus is a beautiful 

 model of a force-pump on an 

 inflnitesimal scale. When the 

 plunger is retracted, it falls 

 into corrugations (fig. 2 a) 

 which are very elastic, and 

 immediately smooth out and 

 bring the plunger back to its 

 original position when the 

 retractor muscles relax. It is 

 possible, though diffîcult, to 

 givea practical démonstration 

 of the working of the syringe 

 under the microscope with a 



moderately high power. The syringe, lying on a slip, cah be 

 held by the stem with forceps in the left hand, and the plunger- 

 rod seized with exlremely fine forceps with the right hand and 

 cautiously worked up and down. The salivary-ducts should be 

 eut as long as possible and a globule of red stain put on theirends, 

 whllst enougli moisture is left on the slip to prevent the lengths of 

 duct from drying-up. The stain can be pumped into the syringe- 

 barrel and forced out of the stem. Some of the smaller Bugs bave 

 a relatively — and in some cases actually — larger syringe than 

 the larger species. 



The smaller lobes of the sausage-shaped salivary- glands (sg, 

 fig. :]) lie in the prothorax. The posterior parts of the larger lobes 

 lie over or alongside the anterior part of the stomach. The two 



