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 chromosme number, is inversely correlated to the length of the foretarsus and consequently to the narrowness of the passages they can frequent.