Lončar, Dragutin, 1. Department of Histology and Embryology, School of Medicine, University of Zagreb, Salata 3, 10000 Zagreb, Croatia; 2. Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, S-106 91 Stockholm, Sweden; 3. Present address: University of North Carolina Chapel Hill, High Point Regional Hospital, Pediatrics 5th Floor, 601 N. Elm St., High Point NC, 27262, USA