If we would gain a true and comprehensive insight into the nature and extent of role of environment in musical life, we must start with some established facts or reasonable assumptions of what is "given" for environment to act upon. The heritage is the capital fund which the environment invests or squanders. Only by knowing the hereditary contributions can we appraise the environmental contributions. In the study of the fruit fly, for example, the revelations of factors which must be regarded as environmental are quite as significant and essential as the revelations about the original organization of genes. The determination of the limits of heredity is the best means for revealing the functions and possibilities of environment. The music geneticist will therefore learn fully as much about environmental influences as he will about hereditary influences in studying heredity. PSYCHOPHYSICAL MEASUREMENTS The music geneticist can approach many significant aspects of the subject through psychophysical experiments for which we now have fairly standardized procedures. For the present purpose, we may call this measurement of the second order as compared with the anatomical and physiological measurements. It proceeds out of, and is a complement to, the anatomical and physiological foundations and probably represents the most fundamental approach from the psychological and musical points of view. These measurements deal primarily with sensitivity and discrimination on the sensory side and the corresponding processes on the motor side. Among them we may recognize two levels: The simple or elemental, in which a specific mental process is related to a relatively specific organic basis; and the complex, which relates to co-operative functions of the elemental capacities. Of the former we have four; namely, the sense of pitch, the sense of loudness, the sense of time, and the sense of timbre--each of which is correlated with a specific attribute of the sound wave, which is the musical medium. We have basic measurements of the hearing of rhythm, consonance, volume, and sonance--all of which represent relatively complex patterns. Each of these complex functions has a unitary character. Rhythm, for example, is not merely time plus intensity; it possesses a unitary character. Because of the difficulty of dealing with the complex patterns, precedence should be given to the four elemental or basic capacities. Excellence in these capacities contributes toward ear-mindedness, of which the auditory image is the most specific characteristic; but at the present time we have no adequate objective method for the measuring of auditory imagery. On the motor side we have corresponding measurements of speed and accuracy in the motor control of each of these factors represented in the sound wave; namely, frequency, amplitude, duration, and form.