142 BYSSIFEROITS MOLLUSCA. 



I have often found it so, and never moored, if placed in a 

 situation where it would be liable to be carried away by the 

 current, averts the fatal wreck by attaching itself by some 

 filaments to the shingle or stones around it.* Of the curi- 

 ous Lepton squammosum my worthy friend Mr. Alder thus 

 writes : — " As may be imagined from the size of the foot, it 

 has the power of crawling about very freely, and sometimes 

 it also swims inverted on the surface of the water in the 

 manner of the Gasteropods, the hinder part of the foot being 

 then unfolded into a disc ; but its favourite position is that 

 of repose, suspended freely in a perpendicular position with 

 the umbones downwards, by three or four threads, so fine 

 that they cannot be seen by the naked eye, and even with 

 a magnifier can only be observed in certain positions of 

 light. The byssal aperture appears to be about the centre 

 of the foot. "f— Even when the species have become ha- 

 bitual spinners, and are rarely found unattached, yet do 

 some of them retain the power to loose their hold, and go 

 in search of another locality. I am certain that this is the 

 case with two of our small Crenellae ; and some years ago 

 Dr. Augustus A. Gould, of Boston, in a letter to me, 

 said : "I have made one observation, which so far as I can 

 learn from books, has not been observed by others. It is 

 generally stated that the Mytili are stationary, and have 

 no other motion than the oscillatory one which their byssus 

 allows. By keeping some in a jar of water I have been 

 enabled to determine that they move from place to place with 

 great facility. The annexed diagram (Fig. 23) may give 

 you some idea of the successive stations they take. Three 

 or four of these stations will be taken in a single night. 

 They detach themselves by casting ofi" the whole of their 

 cables at the gland from whence they all radiate, leaving the 

 distal ends still attached, apparently holding on in the 

 meantime by a single thread till they secure themselves 

 in a new station.";}; 



I must here interrupt the subject by a little space, to tell 

 you how ingeniously man has applied the spinning instinct 

 of the mussels to his purpose:— "At the town of Bide- 

 ford, in Devonshire, there is a long bridge of twenty-four 

 arches across the Towridge river, near its junction with the 

 Taw. At this bridge the tide flows so rapidly that it cannot 



* Forbes an<l Hanley, Brit. Mollusca, i. 386. t Ibid. ii. 101. 



X See also, Proc. Bust. Soe. N. Hist. i. 72. A good figure illustrative of 

 tbese movements of the mussel may be seen in Ann. de.s Sc. Nat. (lf-^42), 

 xviii. pi. 3, fig. A. 1. 



