This is the part of any book where the authors usually discuss why they wrote it. We hope, however, that the text will justifY itself. In fact, any well-trained ecologist will immediately grasp the significance of these seminal works. We have therefore tried to keep our interpretive comments to a minimum. Students of "modern" theoretical ecology will want to contrast the papers in this collection with their modern derivatives. We believe that those who do so will be surprised, if not amazed, by the ecological sophistication and intellectual power of the earlier works. They will stand as a challenge to those who study them, and we hope, provide a standard for the quality of their work. By presenting this collection of works, most of them not easily available and/or for the first time in English, we hope to help them attain the high level of recognition they deserve. We are also enabling readers not sufficiently familiar with Italian to acquire enough of a background to properly follow the works in French not presented here by including Volterra's "Variazioni e fluttuazioni del numero d' indi vidui in specie animali convi venti" (1927), still available. in the original edition.

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Historical Introduction.- I. Logistic Approaches.- Calculus of variations and the logistic curve.- Population growth, equilibria,and extinction under specified breeding conditions: a development and extension of the theory of the logistic curve.- The logistic law and its generalizations (Sur la loi logistique et ses généralisations).- The physiological segregation and the variation of species (Sur la ségrégation physiologique et la variation des espèces).- Conraients on the note by Mr. Régnier and Miss Lambin: Study of a case of microbial competition (Bacillus coli Staphylococcus aureus) (Remarques sur la note de M. Régnier et Mlle Lambin (Étude d'un cas d'antagonisme microbien, Bacillus coli Staphylococcus aureus)).- The integro-differential equations for the toxic contamination of a medium (Sur les équations intégrodifférentielles de la théorie de l'action toxique du milieu).- Comments on the toxic action of the medium relative to the note by Mr. Régnier and Miss Lambin (Remarques sur 1'action toxique du milieu a propos de la Note de M. Régnier et Mlle Lambin (Étude sur le croit microbien en fonction de la quantité de substance nutritive des milieux de culture)).- II. Competition and Predation.- Variations and fluctuations in the numbers of coexisting animal species (Variazioni e fluttuazioni del numero d'individui in specie animali conviventi).- Principles of mathematical biology: Part II (Principes de biologie mathematique: Partie II).- The general equations of biological strife in the case of historical actions.- The growth of mixed populations: Two species competing for a common food supply.- On Volterra's theory of the struggle for existence (Sulla teoria di Volterra della lotta per I'esistenza).- On asymptotically stableperiodic solutions in biological differential equations (Sur les solutions asymptotiques d'équations differéntielies biologiques).- III. Parasitism, Epidemics and Symbiosis.- Contribution to the analysis of malaria epidemiology I. General Part.- Contribution to the analysis of malaria epidemiology IV. Incubation lag.- Symbiosis, parasitism and evolution (Symbiose, parasitisme et évolution (etude mathénatique)).- IV. Genotypic Selection and Evolution.- Mathematical biology. Chapter 15: Evolution (Biologie mathématique. Chapter 15: Évolution).- General differential equations for the problem of natural selection (Équations différentielies générales du problème de selection naturelle).- On the Mendelian coefficients of heredity (Sur les coefficients mendéliens d'hé'rédité).- The differential equations for the problem of natural selection in the case of mutations on sexual chromosomes (Sur les équations différentielles du problème de la sélection naturelle dans le cas de mutation d'un chromosome sexuel).- On the singular points of the differential equations in the problem of natural selection (Sur les points singuliers des équations différentielles du problème de la sélection naturelle).- Natural selection and transformation of the species from the mathematical, statistical and biological points of view (Sélection naturelle et transformation des espèces du point de vue analytique, statisque et biologique).- V. Life and the Earth.- Evolution of the atmosphere: Organic circulation, glacial periods (Évolution de 1 ' atmosphere: Circulation organique, époques glaciares).- General Bibliography.