The cocoon and hatchling of Nais variabilis (Naididae: Oligochaeta)

SUMMARY. 1. The cocoon of Nais variabilis is ovoid with an average length of 527.6±8.4 μm (95% CL) and an average breadth of 378.1±9.9 μm. The cocoon wall is about 7 μm thick and the average volume of the cocoon cavity is 0.035±0.002 mm³. Most cocoons contain one ovum; only single-ovum cocoons developed.
2. Cocoons hatch in about 80 days at room temperature (average 20°C. range 17–23°C). Hatchlings emerged posterior end first and were, on hatching, about one-third the adult live length of 8.5±10.3 mm.
3. It is estimated that adult Nais variabilis are unlikely to produce more than an average of ten cocoons each. Adults ceased asexual budding on becoming nature and died shortly after the completion of cocoon production. There was a brief co-existence of generations.