ACEPHALOUS MOLLUSCA. 
323 
ai1 extensible fleshy organ called, from some of its functions, a foot ; in 
ac t> it has less resemblance to a foot than to a large tongue. It is 
a Muscular mass, capable of being pushed out from between the mantle 
ail( l the valves, and varies much in form ; it is in turn a hatchet, a 
Vf ‘Htilator, a pole, an awl, a finger, and a sort of whip. This foot is 
8lla ple, forked, or fringed. In some species the tissues are spongy, and 
Ca pable of receiving considerable quantities of water. When the organ 
Svv ells, it is elongated and stiff ; on the other hand, by suddenly ex- 
celling all the water, it gets small and pliable, and can now return to 
^ shell. This organ is represented in Fig. 128 ( Donax truneulus, 
in which it is singularly developed. This bivalve is found 
tire sea shore in shallow water; it buries itself almost perpen- 
tl] a^y * n the sands. They are so abundant on the French side of 
e Channel and on the shores of the Mediterranean, that they form 
c °Dsiderable portion of the people’s food. These bivalves have the 
Fig. 128. Donax truneulus (Linntcus). 
^gular power of leaping to a considerable height and then throwing 
^selves to a distance of ten or twelve inches — a spectacle which 
^ a y be witnessed any day at low water. When abandoned by the 
f bating tide, they try to regain the sea. If seized by the hand in 
^ er to drag them out of the sand, aided by their compressed, 
inched, and angular feet, they give to their shell the sudden and 
poetic movement under which the bounding action takes place. 
] fj he shell of the Donax is slightly triangular and compressed ; its 
^h exceeds its height; it is regular, univalve, unequally lateral, 
th' bin g e hears three or four teeth on each valve. The action of 
ese feet is very simple, and is compared by Reaumur to that of 
8 11 ' au placed on his belly who, stretching out one hand, seizes upon 
diff 6 °h.i ec C and draws himself towards it. There is just this 
ah tr, * Ilce > that the movement of the member in the mollusc is 
°gether contractile. 
he molluscs exist in such numbers that our space only permits 
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