The subject of this chapter, unlike Jacobians and Hessians, increases without halt in popularity, the number of relevant writings coming up for report in the new period being a half more than in the period immediately preceding, where the rate of increase had been still higher. A notable feature, too, is the exceptional attention given to Pfaffians, and along with it the growing tendency to view them as entities apart from determinants. Of less importance perhaps but interesting is the first appearance (in 1894) of determinants that are “block” skew.