Dear all, Charles Ehresmann was somewhat reticent about Bourbaki's theory of structures. In fact, he only participated to the first discussions on the "Fascicule de résultats" since he progressively took its distances with the group in the late forties. One of the reasons he gave me for this withdrawal (among others) was that he thought that a good theory of structures should include a theory of "local structures" which has motivated a large part of his earlier works. In several papers in the early fifties, in particular in his 1952 Rio de Janeiro course (reprinted in "Charles Ehresmann : Oeuvres completes et commentées" Part II-1) he briefly recalls the Bourbaki's definition, and then proceeds to develop his own theory of local structures. At this time, he did not know the notion of a category, the interest of which he discovered later through one of his students. It means that categories were not much discussed in France at that time... The first paper where Charles uses categories is the seminal paper "Gattungen von lokalen Strukturen", 1957 (reprinted in the same volume II-1 of the "Oeuvres"). The aim of the paper is to define a general notion of a species of structures and of a species of local structures. For that, he introduces the action of a category C on a set S, calling S a species of structures over C; he proves that it corresponds to a functor F from C^op to Set, and defines the associated discrete fibration, which he calls a "hypermorphism category". Then he defines a species of local structures by internalizing this in the category of local sets (well before internal categories were known ) and gives a "Complete Enlargement Theorem" which translates in this categorical setting the construction of the species of local structures associated to a pseudogroup of transformations. Though the definitions are for general categories, in the last parts he restricts the categories to groupoids. (This 1957 paper has been at the basis of a large part of his/our later works on internal categories, sketches, completion theorems, ) However at that time he said to me that he was not satisfied with the notion of structures, and it led him to develop a more categorical frame while we were in Buenos-Aires in 1958, introducing the notion of "type functors" (in the paper "Catégories des foncteurs types" 1960, reprinted in Volume IV-1 of the "Oeuvres" where is also given the first definition of a double category). His interest of the notion of a species of structures and of "covariant maps" between them has motivated the title of his 1965 book "Categories et Structures" (Dunod). Yours Andree [For admin and other information see: http://www.mta.ca/~cat-dist/ ]