Die Chironomidengattung Pseudosmittia und das Dollosche Gesetz

Abstract

Dollo's law of the non-reversibility of the phyletic development applies to reduced and missing organs as well as to functioning ones which have adapted their shapes to new conditions of living. Such an organ will never again regain its old structure, not even if the old conditions should return. Numerous instances show that this law only applies in general; exceptions prove that it does not apply absolutely, so that it is not really a law, but a rule. 1) The larvae and pupae of Chironomidae live, with relatively few exceptions, in water. Terrestrial species of the Chironomidae are undoubtedly descended from the aquatic. Of the Orthocladiinae-genusPseudosmittia, only species of which the larvae live on the earth were known up to now; the larva of the new speciesPseudosmittia Ruttneri has secondarily reverted to aquatic life. In them a number of their ancestors' adaptations have, it is true, remained intact; two such characteristics, however, have again taken the shape characteristic of aquatic life. So here we have a return to the original phylogenetic stage, as a result of the return of the original conditions of life. 2) The specific pupal organs of the Trichoptera, adaptations to aquatic life, have completely disappeared in the purely terrestrialEnoicyla pusilla, they have partly disappeared in the semi-terrestrial original Trichopterae from the genusBeraea andCrunoecia. (The same holds good for two characteristics of the larvae.) So here, too, we have a return to an original phylogenetic condition. In both cases ”reversibilite de l'evolution”.