A study is made of the history of the type and related concepts, from Greek Antiquity up to the present. It is demonstrated that the type-concept of eighteenth century biology was based on Leibniz's concept of substantial form, and was not related to a Platonic Idea, whilst it is now generally understood in the sense of model or norm. In the present paper, a type-concept is developed which includes ontogenetic and phylogenetic time and various evolutionary mechanisms. This type (an archetype) (...) can serve as a model of the evolutionary potentialities of a taxon, and as a standard of higher classification. All classifications based on the same archetype, whether typological, numerical or phylogenetic, will be comparable, although not necessarily identical. (shrink)

A study is made of some aspects of parallel evolution in Chelicerata. Definitions are given of parallel evolution, convergence, homology and analogy. It is pointed out that the concept of parallel evolution (parallelism) is initially formed in an empirical way, and that a judgment must be based on formal criteria. Particular attention is paid to the rôle of gene regulation in parallel evolution, to the special case of convergence as a result of heterologous regulatory mechanisms, to parallel evolution in homonomous (...) structures (and the superposition of parallelisms and divergences), and to parallelism in the evolution of characters used in higher classification. (shrink)

A comparative study is made of the life-cyle in Chelicerata, and its evolution. Various types of forms or instars, and various evolutionary phenomena are distinguished. They are arranged in a chronological diagram constituting a general model of the evolution of the chelicerate life-cycle. A glossary is added in which terminology is defined.

A study is made of the general principles and theories pertaining to evolution, among which the definition, the evidences, the philosophical roots (the origin of life, the scale of nature, the morphogenetic potentialities), the three models (the Lamarckian, the Darwinistic and an alterative), and a further development of the last-mentioned model.