Oligomerization in Copepoda cyclopoida as a kind of orthogenetic evolutionin the animal kingdom

The morphological-evolutionary notions on oligomerization (i.e., reduction in numbers of segments) of the thoracic limbs and the first antenna in Cope poda Cyclopoida are examined in detail. It is shown that the process of oli gomerization is correlated to a large extent with a decrease in body length . The oligomerization of the thoracic limbs is evolutionarily irreversible, thus capable of channeling the further pathways of morphological developme nt. Consequently, its successive steps in phylogenetic lineages are conside red to represent a kind of orthogenetic evolution.