He observed that the appendicular organs, as he called the leaves, are developed in the same way, whether they be foliageleaves, or parts of the flower, and stated his conclusions thus:
The compound eyes of insects resemble so closely the similar organs in Crustaceans that there can hardly be reasonable doubt of their homology, and the primitively appendicular nature of the eyes in the latter class suggests that in the Hexapoda also they represent the appendages of an anterior (protocerebral) segment.
The most important evidence in favour of their appendicular nature is afforded by the phenomena of regeneration.
The leaf (phyllome) is an appendicular member only borne by a stem, but differing from it more or less obviously in form and development, though co-ordinate with it in complexity of structure.
Klapalek (1904) lays stress on a supposed distinction between appendicular and non-appendicular genital processes.