Abstract
The instars of spiders have usually been determined by measuring the carapace widths. Rearing experiments using three kinds of preys, however, indicated that individual variation in the carapace widths of Xysticus saganus was much larger than that in the length of posterior eye row (LPR), and the frequency distribution of the carapace width for each instar overlapped considerably between different instars. Therefore, more reliable determination of the instars can be made by use of the frequency distribution of LPR, which were not affected by the difference in sexes or food conditions.
