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(1). The fresh-water oligochaete, Aeolosoma hemprichi, hibernates in the form of a cyst.

(2). When the worms are placed in a rich nutritive medium at 6° C., their movements are slowed down, and their growth stops. At this period, chains are formed of two zooids, at the most. Meanwhile, the worm accumulates food reserves, becomes opaque and secretes a mucus which will harden and form a transparent cyst.

(3). The worm stays motionless inside the cyst during the entire cold period. When the temperature increases, it becomes active again, uses up its food reserve and becomes transparent. After about fifteen days, it emerges and resumes its growth according to certain definite laws of scissiparity particular to this species.