and some quotes to help:

First, from Johnson Dictionary(1821 edition)

catgut: a kind of canvas; fiddlestrings

Then from Social New York under the Georges, by Esther Singleton,1902.

The laces and ribbons of the day have already been described with the hats and caps. We must re-member that lace was used for ruffles which were an important finish to the sleeve. Ruffles were also made of the popular gauze and lawn, and were plain, checked, or flowered. " Dresden ruffles" for men and women were advertised in 1754. Gauzes, Paris net and catgut came in colours, as well as in black and white ; and lawns were clear, flowered, spotted, checquered, or of the kind known as " minionet." Hand-kerchiefs were of silk, lawn, satin, linen or gauze. We find them designated as flowered bordered, flowered Kenting, Barcelona, culgee, rosette, satin check, and also made of black and light-coloured gauze, of striped flowered and spotted lawn, of white with flowered borders, and with flowered and striped borders.

from the chapter,Dress Of Women - Gloves, Shoes, And Stays.

And also:

In 1765, Mrs. Thomas Carroll, whose husband had a " mathematical school " in Broad Street, taught " Young Ladies plain work, samplars, French quilting, knoting for Bed Quilts or Toilets, Dresden flowering on Catgut, shading with silk on worsted or Cambrick, Lawn or Holland

from the same book quoted above, chapter entitled "Manners, Food And Culture - Accomplishements"

Mrs Carrol taught her girls to embroider on the catgut-the plain cotton canvas, in patterns of flowers sprigs as found on Dresden china of the period.

The picture above shows a stomacher ,made from emboidered silk, ( not cat gut,sorry,but I'm sure you get the general idea)the stomacher was attatched to the bodice or stays to "bridge the gap" as it were, between the bodice of the open robe.