− | *Gilbert, S.F. (2000); Developmental Biology, 6th ed. Sinauer Associates, Inc, Sunderland MA. | + | *Gilbert, S.F., 2000; Developmental Biology, 6th ed. Sinauer Associates, Inc, Sunderland MA. |
| + | *Sjaastad, OV.; Hove, K. & Sand, O., 2003. Physiology of Domestic Animals. Scandinavian Veterinary Press, Oslo. (735pp). |