Abstract
SUMMARY. L 266 degree‐days, above a threshold of 1.0°C, were required for cocoons from the triclad Dendrocoelum lacteum to hatch. The relation is described by ln D=6.12–1.17 1nr (D=number of days, T= temperature). Laboratory and field cocoon deposition reached a maximum in late April; peaks of hatchling occurrence were 2 weeks later. The number of hatchlings per cocoon and eocoon viability declined as spring proceeded. Cocoon deposition ceased in June, coincident with regression of the reproductive organs of the adults. Newly hatched triclads in the field are thought to avoid stones for their first weeks. It is suggested that the earlier and more abundant offspring production in South Sweden than in Britain could be attributed to differences in spring temperature conditions.
Published Version
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