254 HUXLEY, ON THE MOUTH OF THE SCORPION. 



aperture. The inner surface of the chitinous lining of the 

 pharynx is more or less rugose ; and, towards the oesopha- 

 geal aperture, presents a number of very minute spines (fig. 6) . 



The transverse muscular fibres (fig. 2 n), rightly said by M. 

 Blan chard to arise from the forks of the apodeme (?»), are 

 inserted into the side Trails of the pharyngeal sac, which is so 

 narrow from side to side, as readily to escape notice, without 

 dissection. The termination of the aorta appeared to me to 

 pass between the two superior crura of the sac. 



The large vertical muscles (fig. 1 q) are, as M. Blanchard 

 states, inserted into the base of the apodeme ; and, besides 

 these, the labrum is traversed by strong transverse and longi- 

 tudinal muscles. 



The mode of action of this curious apparatus appears to be 

 readily intelligible. Scorpions, as is well known, suck the 

 juices of their prey, and the pharyngeal sac seems to be 

 w r ell calculated to 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 at the sides, and the 

 processes furnished by the maxillary limbs below r , and that 

 the minute oral aperture is applied to a wound. Then, 

 if the transverse muscles (ti) contract, the sides of the pha- 

 rynx 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 (p ) is brought down 

 over the oesophageal aperture, regurgitation from the oeso- 

 phagus will be prevented; but, in any case, as the oral 

 aperture is larger than the oesophageal, 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 oesophagus. Successive repetitions of the action 

 would gradually pump the juices of the prcyinto the alimentary 

 canal of its captor. 



