John Morton, The Natural History of Northamptonshire, Londres, R. Knaplock, 1712, p. 412-413.
9. Water Insects that cover themselves with Cases, have either a Case.
Immoveable, being affix’d to Pebbles or Others stones. This sort of Case is ordinarily compos’d of Gravel and Sand agglutinated : and is of a roudish Shape. Dr. Plot has given a particular Account of one Variety of them in Natural History of Oxfordshire, ch. 7. #. 25. We find the same in the Stoney Brook nigh Kettering, and in several others.
Or a Moveable migratory one, which is commonly called a Cad-Case : Either
Round and long, having either
Straws, and sometimes Bits of Sticks, agglutinated ; and those either
Parallel, of which are two Species, a larger one two Inches long, and a smaller one, the commonnest of all :
Transverse and shorter than the former ; wherewith in some of the Cases are interlaid very small Stones, in others small Snail-Shells : or
Perpendicular, I now speak of the outwarder Straws which compose this sort of Case, which are sharp, stiff, and very slender little bits set End-ways, like the Prickles of a Hedge-hog when erected. This Species occurs but seldom, and was unknow to Mr. Willougbby, as were also four or five more of the Varieties that follow.
Seed-Vessels, and Seeds of Plants.
Snails-shells of various Kinds, and a few small Stones intermix’d.
This sort of Case is very pretty with that Variety of Shells that usually adhere to it.
Fragments of Snail-shells, with a Mixture of fine Sand.
The smaller Pebbles and Flints with a little Sand.
Sand of a coarser Grit. These Two last are very common Sorts, and occur in almost every Brook, even in those Brooks where thee’s not the smallest Heap or Parcell of Sand to be seen in any part of them ; as at Oxendom, and elsewhere.
Within these are the Worms call’d Cod-Bait.
Sand of a finer Grit. Some of these are crooked and tapering, not unlike to a Cock’s Spur : Others are tapering, of a Conical Shape, and are not crooked. They vary in Colour, as do also the former.
A Stoney Matter, which is brought out of the Earth by the Water of those called Petrifying Springs, andwhich, as the Water glides along, is catch’d and entangled in a flimy Matter upon and about the Bodies of the Cad-worms which are by Nature directed to post themselves for that very Purpose, in the Chanels of those Springs. There are Cad-cases of this Sort in several of our Petrifying Waters, at some Distance from their Sources. I first discover’d the way of their Formation in the Chanel of a Small Rill, that carries down one of these Springs, betwixt the Bog-Close at Harrington and Rowel Field, above the little Bridge that leads into the Field ; where there are many Incrustations, otherwife called Petrifactions, consisting of the same Stoney Matter, as do the Cad-cases there. These are a coarser Grit. In a Rill or Gutter betwixt Bulwick and Blaterwick, I oberserved a Variety compos’d of a Matter as fine and as White as is that or out Whitest Limestone.
Common Sand with Two or Three Parallel Straws, or slender Pieces of Sticks affix’d to the Outside of it. There are usually no more than ; Two of these Sticks, and those set opposite to each over Sideways. So placed they much conduce to the strengthning of the Case.
Or Flat and Compressed,
With somewhat biger Stones adhering to the Sides of the Case, never to the Fore or Back-part of it ; whence it necessarily appears flat or compressed : or with no Stones adhering thus to the Sides, but with a Case running sorth Sideway into a thin Margin, as it were Wings. ‘ Tis a s slatter and more compressed Case than the former, and also tapering.
10. We meet with all these Sorts or Varieties of Cad-worm Cases in the Ponds, Brooks, or Rivers of this County. Indeed a greater Variety there is of them, than of the Insects that carry these their little Houses about with them. For the same Sort of Insect, tho’ they do not vary much in the Form or Figure of their Houses, yet as to the Materials of them they do, In some Places building them of Sand : in others where there is no Sand, but abundance of Small Shells, of these : in others of a Chalky or Calcarious Matter, or whatever else Place assords, that’s fit for the Purpose.
11 The Ground-work, if I may so call it, of all the Cases is a glutinous or slimy Matter, or such Tenacity and Strenth, that I have seen Two pretty large and weighty Pebbles, so closely conjoin’d with this slimy Substance proceeding from a Cad-worm, that had plac’d it self betwixt them, that they would not fall afunder one from another : Nothing but Violence would fever them. And when I pluck’d them, it Drew forth a Rope of Slime from out the Cad-case, much like the Saliva of Snails. Heroes the Cad-worm forms it self a looké Kind of Coat, covering all, unless the Head and Feet, which are set on near the Head. These the Cad can exert or draw in at pleasure : and by means of this Sort of Gluten, to which every little Body that touches it adheres, the Animal rough-Coats, and strengthens that Coat with Sand, Straws, or other proper Matter, just to much of them usually as serves to give a due Fimness to the Coat, without rendring it too bulky and cumbersome. The other Extremity that’s opposite to the Head, is closed wich such Matter as the Sides of the Case are composed of. Which closed End the Cad-worm, when she sees a Gudgeon, a Fish that delights to prey upon them, about to assault him, erects, striking his Head into the Bottom of the Brook or River : and having put himself into this Posture, the Gudgeons give over the Assault.