MOLLUSCA ACEPHALA. 203 



converting it into a canal. The glutinous secretion, 

 which is poured into this canal, dries into a solid 

 thread ; and when it has acquired sufficient tena- 

 city, 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 

 surface of that object. The canal of the 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 different directions around the shell. Sometimes 

 the attempt fails in consequence of some imperfec- 

 tion in the thread ; but the animal, as if aware of 

 the importance of ascertaining the strength of each 

 thread, on which its safety depends, tries everyone 

 of them as soon as it has been fixed, by swinging 

 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 appear to have the power of 

 cutting or breaking them off. The liquid matter 

 out of which they are formed is so exceedingly 

 glutinous as to attach itself firmly to the smoothest 

 bodies. It is but slowly produced, for it appears 

 that no Pinna is capable of forming more than 

 four, or at most five threads in the course of a day 

 and night. The threads which are formed in haste, 

 when the animal is disturbed in its operations, are 

 more slender than those which are constructed at 

 its leisure. Reaumur, to whom we are indebted 

 for these interesting observations, states also that 



