thei7' Food and Digestive Organs, 



411 



tracting in regular succession, they force it out beyond the 

 lips, in a manner perfectly similar to the evolution of the ten- 

 tacula of the snail. There is, in particular, one muscle, near 

 the place where the exterior muscle is attached to the head, 

 which is stronger and more effective in this operation than all 

 the others. When extended, the proboscis can be bent to 

 all sides, and at any point, by the action of the retractor 

 muscles, parcels of them acting, while others assume the place 

 and office of antagonists. The Jigs. 51, 52, and 53. will serve 



to illustrate this interesting mechanism. In j%. 51. the pro- 

 boscis is retracted about a half: the external cylinder [a) is 

 seen enveloping a portion of the inner (Z>), the end of which 

 [c) is the end of the proboscis : the muscles which draw it 

 within the body (d d) are in a state of contraction, and at e 

 we see the great annular muscle, the use of which is to push 

 forwards the inner cylinder, and consequently lengthen the 

 organ. In Jig. 52. this muscle, and all the annular fibres, 

 have by their action greatly protruded the proboscis, and 

 its retractor muscles {d d) are extended and laid bare ; the 

 exterior cylinder (a) has become very short, and the interior 

 {b) is proportionably lengthened. Fig. 53. 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 aoparatus [e e), the salivary 



