The summer of 1952 was rather dry and probably masked any inherent rhythm of biological activity possessed by the species Eisenia rosea. Data presented do underscore the influence of soil moisture upon activities and population density of earthworms, as well as the need for continuous records of soil moisture in order to demonstrate the moisture "season." It is improbable that specific moisture levels, in terms of percentages, can be used to express toleration limits even in soils of equivalent physical structure and texture. Part of the variation in population density of Eisenia rosea occurring between collection sites may have arisen from the so-called biotic potential of the species. The absence of E. rosea from wide areas, however, indicates inadequacy of the soil environment. Several soil factors, including temperature, were found to be reasonably uniform; the moisture regime, on the other hand, showed marked differences. The latter must be described in terms of the amount and length of time soil moisture is available. The qualitative structure of the earthworm population was also related to these variations in soil moisture. The considerable fluctuation in earthworm numbers from season to season was caused by: (1) migration of larger individuals from the upper soil to lower depths, (2) emergence of young from cocoons, (3) mortality, and (4) dispersion. Vertical movements of oligochaetes can be obscured by improper sampling methods; the rate and time of emergence of young worms may be shifted by the prolongation of cocoon life possible in this group of organisms when external soil conditions are unsatisfactory. A decline in soil moisture induced worms of the species E. rosea to coil up, evacuate the gut, and enter a state of quiescence. No evidence was obtained to indicate that this condition was obligatory; lowered soil temperatures were found to prolongue the inactive period. Appearance of posterior regeneration in this species was coincident with the onset of quiescence and possibly only occurs during such periods. Analysis of the population of E. rosea from the standpoint of individual growth rate was difficult because of the seasonal migration of large worms into deeper soil layers. Thus, a high percentage of the population during summer; fall, and early winter months was composed of smaller worms. Growth of these worms and a return of the larger individuals to the upper soil, resulted in a percentage decline of small earthworms during February, March, and April, 1953. Sexual development, as evidenced by the presence of a clitellum, followed the cycle of activity. During the season of 1952-53, this cycle was related primarily to soil moisture and secondarily to temperature. Any inherent sexual rhythm possessed by the species Eisenia rosea was probably masked by dry soil conditions.