Development

(-věl'up-měnt.) [Fr. développement.] (Math.) That proce by which a term or quantic is converted into another of a larger form, but of corresponding value or definition.-(Physiol.) In order to become thoroughly acquainted with the nature of an organism, it is nece ary to study its life-history, and to trace its D. as it pa es from the embryonic to the adult condition. Morphology, it has been said, teaches us what an animal is, physiology what it does, the study ofD. what it was, and how from what it was it came to be what it is. This study is also nece ary for the determination of its homologies (see HOMOLOGY), because it is not always safe to infer homology in organs from a correspondence in structure and position. An examination of the organs in their simplest state, and in the stages they pa through, is required to determine the point with perfect certainty. A comparison of the forms of organized beings in past times with one another, and with those now existing, has led some naturalists to conceive that there has been a gradual pa age from one form to another, that is, from beings of alo wer to those of a higher grade; in other words, that the influence of external circumstances acting through along lapse of ages upon beings po e ing indefinite variability, has changed the earlier le complex forms of life into forms of greater complexity. It is a fact that existing beings of the highest type now pa during their lives from a structure of the greatest simplicity to one of the greatest complexity; and it has been thought that the study of fo il remains proves that the history of organic life, from its first appearance on the planet to the present day, has pursued an analogous course. This is the theory of progre ive development. [s. 281]