PROBOSCIS OF BTJCCINUM. 



543 



Fig. 273. 



in the Pectinibranchiate Gasteropods ; and with its assistance these 

 animals can bore through the hardest shells in search of food, making a 

 hole as round and smooth as if it had been made by a drill of human 

 contrivance. It is from Cuvier we again borrow the subjoined descrip- 

 tion of this unique apparatus*. 



(1440.) The proboscis of Bucdnum is organized with marvellous 

 artifice. It is not simply provided, like that of the elephant, with the 

 means of flexion and extension, joined with a limited power of contrac- 

 tion and elongation, but it can be entirely retracted into the body by 

 drawing itself into itself in such a manner that the half of it which 

 forms its base contains and encloses the half nearest its point ; and it 

 can protrude itself from its sheath thus formed, by unrolling itself like 

 the finger of a glove, or like the horns of the garden snail : only it is 

 never completely retracted, but always remains more or less folded upon 

 itself. : tf 



(1441.) It may be represented as being composed of two flexible 

 cylinders, one contained within the other, as shown in the annexed 

 figure (fig. 273), the upper edges (i i) of the 

 two cylinders being continuous in such a 

 manner that by drawing out the inner cylinder 

 (b b) it becomes elongated at the expense of 

 the other, and on pushing it in again it be- 

 comes shorter, while the outer cylinder (&) is 

 lengthened by adding to its upper margin. 



(1442.) The reader must now imagine a 

 multitude of longitudinal muscles (d d), all 

 very much divided at both their extremities, 

 and attached by one end to the parietes of the 

 body, whilst by the opposite they are fixed to 

 the interior of the inner cylinder of the pro- 

 boscis (b) along its entire length and as far as : 

 its extremity. It is evident that the action of 

 these muscles will retract this cylinder, and 

 consequently the entire proboscis, into the 

 body. 



(1443.) When thus retracted, a great part of 

 the inner surface of the internal cylinder (6) 

 will necessarily become a portion of the external surface of the outer 

 cylinder (fc), and the contrary when the proboscis is protruded. It is 

 in consequence of this that the insertions of the muscles (d d) vary in 

 position. 



(1444.) The protrusion of this proboscis is effected by the action of 

 the circular muscles that form its walls. 



(1445.) When the proboscis is extended, the retractor muscles 



* " Memoire sur le grand Buccin (Bucdnum undatum}, et sur son Anatomic." 



Proboscis of Bucdnum. 



