MOLLUSCA ACEPHALA. 165 



ployed. This mould is curiously constructed; there is a 

 deep groove which passes along the foot from tlic root of the 

 tendon to its other extremity; and the sides of this groove 

 are formed so as to fold and close over it, thereby convert- 

 ing it into a canal. The glutinous secretion, which is poured 

 into this canal, dries into a solid thread; and when it has ac- 

 quired sufficient tenacity, the foot is protruded, and the 

 thread it contains is applied to the object to which it is to be 

 fixed; its extremity being carefully attached to the solid sur- 

 face of that object. The canal of ^thc foot is then opened 

 along its whole length, and the thread, which adheres by its 

 other extremity to the large .tendon at the base of the foot, 

 is disengaged from the canal. Lastly, the foot is retracted, 

 and the same operation is repeated. 



Thread after thread is thus formed, and applied in diffe- 

 rent directions around the shell. Sometimes the attempt 

 fails in consequence of some imperfection in the thread; but 

 the animal, as if aware of the importance of ascertainino- the 

 strength of each thread, on which its safety depends, tries 

 every one of them as soon as it has been fixed, by swingino" 

 itself round, so as to put it fully on the stretch: an action 

 which probably also assists in elongating the thread. When 

 once the threads have been fixed, the animal does not ap- 

 pear to have the power of cutting or breaking them off. The 

 liquid matter out of which they are formed is so exceedino-- 

 ly glutinous as to attach itself firmly to the smoothest bo- 

 dies. It is but slowly produced, for it appears that no Pin- 

 na is capable of forming more than four, or at most five 

 threads in the course of a day and night. The threads that 

 are formed in haste, when the animal is disturbed in its ope- 

 rations, are more slender than those tliat are constructed at 

 its leisure, Reaumur, to whom we are indebted for these 

 interesting observations, states, also, that the marine muscles 

 possess the art of forming these threads from the earliest pe- 

 riods of their existence: for he saw them practising it, when 

 the shells in whicli they were enclosed were not larger than 

 a millet seed.^ In Sicily, and other parts of the Mediter- 



• Memoircs de I'Acadcmic des Sciences: 1711, p. 118 to 123. Poli con- 



