Concerning the progressive change in the distribution pattern, the censuses on the eggs, larvae and pupae of Pieris rapae crucivora BOISDUVAL in a cabbage farm were made successively during the period from June to July of 1953 in every plant. The results are as follows : 1. The distribution pattern tends to change from concentrating to random with the hatching of eggs and larval growth and this change is remarkable between the eggs and the first instar larvae. 2. The hatching rate has no relation to the density. On the assumption that the hatching occurs at random with equal rate in every plant, a close agreement between the observed frequency distribution of the hatched eggs and the theoretical one is recognized in the comparison between them. 3. In the case where the distribution of the eggs on a plant conforms to the POLYAEGGENBERGER distribution and its contagious parameter is d, the coefficient of diversity, s^2/x^^- is given by(1+d), therefore, when the hatching of eggs occurs equally in each plant and its probability is p, the value of s^2/x^^- in the distribution of the hatched eggs is given by(1+pd). Namely, when the value of p decreases, the value of s^2/x^^- approaches to 1 and the distribution of the hatched eggs approaches to the POISSON distribution. 4. The movements of larvae among the plants are observed after the third instar but most of them are limited among the neighbouring plants. In the case of the last instar larvae, most of them emigrate from the observed farm for the pupation. 5. As the peak of the number of individuals in eggs and each instar larvae appears at intervals of two to four days, it seems that the time length required for the growth of each stage is almost the same in each individuals. The rate of molted larvae in each instar does not differ statistically among the plants of different density. 6. The mortality of larvae has no relation to the density but in some cases it has a tendency to be inverse density-dependent. Therefore, it is impossible to suppose that the approach of the distribution to the random pattern is caused by the mortality. The progressive change of the distribution pattern with larval growth may be based on the stochastic process as stated in the case of hatching.
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