Karyotypes and habitat interrelations among soil Arthropoda: Collembola and Protura

In five species of Onychiurus (Collembola Onychiuridae) the diploid chromosome number is higher in animals of narrower width. In three species of Acerentomon (Protura Acerentomidae) the number of the chromosome arms (FN), not the chromosome number, is inversely correlated to the length of the foretarsus and consequently to the narrowness of the passages they can frequent. These correlations are discussed from the point of view of the animal's habitat, of the karyotypes of other species of the same family, and of some morphological characters of the adults.