THEIR PROBOSCIS. 



309 



muscle, the use of ^which is to push forwards the inner 

 cylinder, and consequently lengthen the organ. In Fig. 58, 

 this muscle, and all the annular fibres, have by their action 

 greatly protruded the proboscis, and its retractor muscles 



Fig. 58. 



Fig. 59. 



(d d) are extended and laid bare ; the exterior cylinder (a) 

 has become very short, and the interior (b) is proportionably 

 lengthened. Fig. 59 represents the two cylinders cut up in 

 a longitudinal direction to show what they contain, and in 

 what manner the retractor muscles are distributed upon the 

 inner parietes. In the inner cylinder we find the tongue, 

 with all its apparatus (e e\ the salivary canals (//), and the 

 greater portion of the gullet (g g) : the tongue is a very 

 narrow cartilaginous membrane, armed with numerous acute 

 spines or prickles curved backwards ; and the principal pur- 

 pose of the elongation of the proboscis is seemingly to carry 

 its rough point to the body which the snail wishes to perfo- 

 rate and suck.* 



And this " rough point" is sufficient of itself to do the 

 work without the concurrence of any hypothetical solvent, 



* Cuv. Mem. xvii. 7. 



