The phrase 'same structural series' [...] identifies a series of forms which are structurally related, both by contrast with other series and by virtue of their having certain common features.
- Nida (1949), a pag.42

A structural series consists of a single internal distribution class or of multiple distribution classes united by means of supplementary or complementary morphemes. For example, the past-tense and the plural formations in English constitute two structural series, each containing supplementary morphemes.
- Nida (1949), a pag.110

Structural series in which there are no subclasses of determiner or determined immediate constituents are very simple. In English there are two such formations: (1) the noun formation with agentive '-er', e.g. 'dancer', 'player', 'walker', 'worker', 'flier', 'beginner', and (2) the verbal formation with '-ing', e.g. 'dancing', 'playing', 'walking', 'working', 'flying', 'beginning'.
- Nida (1949), a pag.112

Several fundamental principles of description should be noted: 1. A structural series is described on the basis of immediate constituents. 2. The determiner immediate constituent is noted first. 3. The distribution of the determiner immediate constituent is described in terms of the determined immediate constituent. 4. The determined immediate constituents may be identified as follows: a. By listing b. By reference to a previously listed class, with or without exceptions.
- Nida (1949), a pag.112