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1. Among the species of the Carabid genus Pterostichus different types of annual periodicity can be found. P. cupreus and P. coerulescens were investigated as representatives of spring breeders with summer larvae (hibernating as adults) and P. vulgaris as a representative of autumn breeders with winter larvae. 2. The female spring breeders enter dormancy, irrespective of the photoperiod. This can be overcome by successive treatment with short-day followed by longday in continuous warmth (photoperiodic parapause). In the field the increasing length of day in spring terminates the parapause. In both species the percentage of mature females depends on the duration of short-day treatment. After eight weeks of short-day the percentage of females with ripe eggs reaches maximal values of up to 100%. By a repeated treatment with first short-day and then long-day old females can be stimulated to a second development of ripe eggs. A temporary drastic lowering of temperature for four months terminates the parapause of the females even under constant photoperiods (continuous short-day or long-day), but under these conditions less than 40% of the females of P. coerulescens and less than 20% of those of P. cupreus mature. The parapause in females can also be terminated by raising the light intensity under constant short-day. In this case, however, only 33% of the females of P. coerulescens became ripe. 3. Not more than 25% of the males of both species of spring breeders mature under continuous warmth after a change from short-to long-day. They do mature, however, when short-day treatment is combined with cold. If the influence of cold and short-day is prolonged from 2 to 4 months and if the temperature is lowered from +5\2-7\dg to +2\2-3\dg the percentage of mature males rises steeply (up to more than 80%). Females from laboratory cultures paired with males treated with cold and short-day are much more prolific than those paired with males which have been treated with warmth and short-day. The dormancy of a high percentage of the males of P. cupreus in warmth can also be terminated in continuous long or continuous short-day by temporary lowering of temperature (thermic parapause). Males of P. coerulescens mature due to changing temperatures only in continuous short-day, but not in long-day. 4. In warmth, development and metamorphosis of both the spring breeders under investigation takes place under short-as well as under long-day. Mortality is equal in both cases. The duration of development is prolonged in both species under long-day. 5. The adults of both sexes of the autumn breeder P. vulgaris mature irrespective of the photoperiod. They show no dormancy. 6. The larval development ofP. vulgaris is indepent of the photoperiod. In warmth, the 2nd or 3rd instar falls into a form of dormancy which will be called a thermic parapause of the larvae, because it can be terminated by a temporary treatment of the 3rd instar with cold.