Where in Gauss's nachlass did he pose the problem of connectedness of a surface?

On p.98 of the book "Mathematics of the 19th Century: Geometry, Analytic Function Theory", the authors mention a note written by Gauss in 1840:

In 1840 Gauss wrote a note in which he introduced the concept of one- and two-dimensional manifolds, which he called a "line" (Zug) and a "layer" (Schicht), and posed the question of the decomposition of a "layer" bounded by several "lines" into several "layers" bounded by one "line". What is actually involved here is the problem of connectedness of a surface, later solved by Riemann and subsequently became one of the most important problems of combinatorial topology."

My question is mainly about getting references. I tried to search for it in volumes 8, 10 and 12 (i think it's most likely to be found in these volumes). Can anyone help locate it in his writings?