[Developmental rate and life cycles ofMesostoma productum (O. Schmidt, 1848) (Turbellaria, Neorhabdocoela)].

Under laboratory conditionsMesostoma productum produces a batch of dormant eggs subsequent to a batch of subitaneous eggs. In nature only a few individuals change from dormant egg production to subitaneous egg formation in one batch of eggs.The interval between hatching of the mother and hatching of her young from subitaneous eggs is 24.5 days at 15° C, 16.7 days at 20° C and 13.2 days at 25° C. These values are about 13,9 and 7 days lower than those forM. lingua.The life-cycles extended over 3 months in 1968 and over 4 months in 1969 and 1970. The first generation hatching from dormant eggs only produces subitaneous eggs. All further generations hatch from subitaneous eggs. Under optimum conditions of 20° C the population produces subitaneous eggs. Average temperatures of 25° and 15° C cause dormant egg formation by a high percentage of the animals. Towards the end of the life-cycle the majority of eggs formed are dormant.From the middle of May to mid-September 7 generations occur inM. productum, whereas inM. lingua the same number of generations occurs in 7.5-8 months.