The old threads were found to differ materially from those newly spun, the latter being whiter, more glossy, and transparent than the former, and it was thence discovered that it was not the office of the tongue to transfer the old threads one by one to the new spots where they were fixed, which course M. Réaumur had thought was pursued. The old threads once severed from the spot to which they had been originally fixed were seen to be useless, and that every fibre employed by the fish to secure itself in a new position was produced at the time required; and, in short, that nature had endowed some fish, as well as land insects, with the power of spinning threads, as their natural wants and instincts demanded. This fact was incontrovertibly established by cutting away, as close to the body as they could with safety be separated, the old threads, which were always replaced by others in a space of time as short as was employed by other muscles not so deprived. “The pinna and its cancer friend” have on more than one occasion been made subjects for poetry. There is doubtless some foundation for the fact of the mutual alliance between these aquatic friends which has been thus celebrated; yet some slight coloring may have been borrowed from the regions of fancy wherewith to adorn the verse, and even the prose history of their attachment may be exposed to a similar objection. The scuttle-fish, a native of the same seas with the pinna, is its deadly foe, and would quickly destroy it, were it not for its faithful ally. In common with all the same species, the pinna is destitute of the organs of sight, and could not, therefore, unassisted, be aware of the vicinity of its dangerous enemy. A small animal of the crab kind, itself deprived of a covering, but extremely quick-sighted, takes refuge in the shell of the pinna, whose strong calcareous valves affords a shelter to her guest, _while he makes a return for this protection by going forth in search of prey_. At these intervals the pinna opens her valves to afford him egress and ingress: if the watchful scuttle-fish now approach, the crab returns instanter with notice of the danger to her hostess; who, timely warned, shuts her door and keeps out the enemy. When the crab has, unmolested, succeeded in loading itself with provisions, _it gives a signal by a gentle noise at the opening of the shell_, and when admitted, the two friends feast together on the fruit of its industry. It would appear an arduous, nay, a task almost impossible for the defenceless and diminutive crab, not merely to elude its enemies and return home, but likewise obtain a supply of provender sufficient to satisfy the wants of its larger companion. The following different account of the nature of this alliance is more credible:--