The origin of evolutionary novelties is a long-standing issue in evolutionary biology. Changes in developmental processes and mechanisms must underlie novel anatomical structures, but exactly how this works is a much more difficult question. I propose to investigate this, based on a literature survey and data from two empirical research projects presently conducted in my lab, one on the role of FoxN3, the other on the role of bagpape genes for the development of unique larval head skeletal structures in frog tadpoles. Experimental work on the effects of knock-down of these genes on both the anatomical development and on the expression of genes belonging to the genetic regulatory network (GRN) have yielded a wealth of empitical data that now needs to be put in a wider discussion of the evolution of anatomical noveltis and their underlying gene regulatory mechanisms. FoxN3 knock-down has been shown to remove several unique larval structures only found in frog tadpoles, such as the elaborate, filigreed structure of the gill basket necessary for filter feeding, and the extra mouth structures present as unique novelties in frog tadpoles and especially well developed in tadpoles grazing algae. Knock-down of the bagpipe gene Zax has severe effects of the development and anatomy of a major novelty, the rostral cartilages, in frog tadpoles. How did FoxN3 and bagpipe genes, or the genetic network that they are part of, gain this new function? What is the actual mechanism of "recruitment" or "co-option" in this case? Based on such detailed empirical data, it should be possible to develop a general model for the evolution of anatomical novelties. During my visit, I will write a synthetic review paper that tries to deepen and sharpen our understanding of the origin of evolutionary novelties.