The life cycle of the spider Thomisus onustus, with its two adult phases annually, is elucidated. Differences between males and females, in the length of the developmental period up to maturity, excluded the possibility that siblings could mate in nature. Females maintain a stable cycle of one year, whereas the males show a change in the length of their developmental cycle, according to the phase from which they originate. The variance which occurs among spiderlings, in regard to the number of moults and the length of the different instars is discussed.
Outlines for a general classification of the life histories of spiders is being suggested.