AND PHARYNX OF THE SCORPION 399 
perform the part of a kind of syringe. For, suppose the prey to be 
held between the labrum above, the bases of the great mandibles of 
the sides, and the processes furnished by the maxilliary limbs below, 
and that the minute oral aperture is applied to a wound. Then, if the 
transverse muscles (7) contract, the sides of the pharynx will be 
drawn apart, and a partial vacuum, or at least a tendency to the 
formation of one, will be created. If, by the same action, the 
projection (pf) is brought down over the cesophageal aperture, regurgi- 
tation from the cesophagus will be prevented ; but, in any case, as the 
oral aperture is larger than the cesophageal, it will be easier for the 
sac to be filled through the mouth. The sac being full, if the labrum 
is depressed so as to close the oral aperture, and the transverse 
muscles are relaxed, the elasticity of the walls of the pharynx will 
tend to reduce its cavity to its primitive dimensions, and hence to 
drive the ingested liquid into the cesophagus. Successive repetitions 
of the action would gradually pump the juices of the prey into the 
alimentary canal of its captor. 
PLATE XII. [PLATE 31]. 
Fic. 
1.—Longitudinal vertical section of the cephalo-thorax of a Scorpion, showing the 
pharynx, cesophagus, nervous centres, and the large eyes in their natural relations. 
2.—Dorsal view of the cephalo-thorax of a Scorpion, opened and dissected, so as to show 
the apodemata, and the anterior portion of the alimentary canal, with the pharyngeal 
muscles. 
3.—The chitinous lining of the anterior part of the alimentary canal, the integument of the 
labrum, and the basal processes of the first maxilla. 
4.—The chitinous lining of the pharyngeal sac, viewed from above. 
5.—A transverse section of the same, taken along the line x y (fig. 3). 
6.—The region of the pharyngeal sac near the commencement of the cesophagus. 
The letters have the same significations throughout :—«, mouth; 4, labrum ; ¢, pharynx ; 
d, cesophagus ; ¢, salivary duct; 7, diaphragm ; g, eye and ocular nerve; #, subceso- 
phageal ganglion; z, antenna; 4, maxilla; /, mandible ; ™, apodeme ; 7, pharyngeal 
muscles ; v, sub-oral transverse thickening of the chitinous integument ; 9, valve (?) of 
the pharynx ; x y, line along which the section in fig. 5 is taken. 
